Why do people do what they do?
A look at all the factors affecting how a person thinks, behaves, and feels.
We see clients who want to change the way they feel – they’re stuck, depressed, etc. We see clients who want to change how they behave – they want to become non-smokers or be able to give that presentation. And we see clients who want to change the way they think – they want to reduce compulsive behaviours associated with OCD (obsessive-compulsive disorder) or they want to get over a phobia.
A person’s thoughts, feelings, and behaviour are affected by more than just what happens in their brain. So, I thought I’d look at why people do what they do.
All we ever see is what people look like, what they do, and how they react to what’s going on. From that, we try to infer their mood and we attempt to predict how they will behave in future. We might even guess at what they were thinking when they acted in the way they did. And, quite possibly, we’ll try to work out what their beliefs might be that led them to be the way they were. In this article, I want to look at the two-way links between the brain and body affecting how a person thinks, feels, and behaves.
So, what factors do make people behave, feel, and even think the way they do?
Let’s start at the beginning. People start off the way they are because of their genes – a random mixture from both parents. In addition to how the genes are expressed, there are also the effects of epigenetics. This is where the expression of a gene or genes is altered, but the basic genetic code doesn’t change. As scientists discover more about genes, we find some that definitely have a specific impact on a person – eg genes for particular diseases – and there are suggested associations between genes and certain things, eg addiction or depression.
Do genes control how happy a person will be? Sonja Lyubomirsky, author of The How of Happiness suggests that 50 percent of happiness is genetically predetermined, while 10 percent is due to life circumstances, and 40 percent is the result of your own personal outlook (see Figure 1). This figure might apply to more than just happiness.
Figure 1: Lyubomirsky’s happiness pie
It’s worth noting that nowadays these figures are often criticized for overstating the precision. In addition, heritability estimates for wellbeing vary substantially depending on population and methodology, and heritability is not fixed across environments. Lastly, the 40% intentional activity figure has weak empirical support as a stable proportion.
The second big thing that affects a person is their environment. This is the surroundings or conditions in which a person lives or operates.
The effects of genes and environment led to the nature-nurture debate that went on for many years. And this fits Lyubomirsky’s ideas about happiness levels.
We also know about US soldiers in the Vietnam war who took addictive opium while in Vietnam, and how the majority of them just stopped when they returned to their families in the USA. Their environment changed and so did their behaviour.
We also know that a person’s childhood can affect how they think and behave as an adult, and also affect their health as an adult and their life expectancy. It’s also during childhood that many people’s core values and beliefs are created (or indoctrinated – depending on your beliefs).
We help clients who experience butterflies or worse with nerves or excitement at the thought of giving a presentation and many other activities. These can be affected by their expectations of what will happen – or their lack of information about what will happen.
And we see people looking for help with IBS (irritable bowel syndrome) and other gut-related issues. So, let’s move our focus to our GI tract and the trillions of microorganisms that live in it – our gut microbiome. And let’s look at the two-way link between the brain and gut – the gut-brain axis (GBA). Our gut has to digest food (ie make and secrete enzymes). It has to absorb food. It has to squeeze food through itself (peristalsis). And it has to defeat invading bacteria. It has to ensure the cells in the lining keep the bad stuff out and let the good stuff through. It has to not have too thin a layer or too many gaps between cells. And it has to produce a layer of mucous over the top of this lining. And your microbiome helps – it does use some of your food, but it does create useful products. If you don’t have a microbiome, eg through taking too many antibiotics, you’ll not be very healthy.
What you eat can affects your biome. Studies have shown that gut microbes can affect behaviour and even emotions (like depression). A Belgian study found two kinds of microbe (Coprococcus and Dialister) were missing from the microbiomes of their depressed subjects, but not from those with a high quality of life.
Compounds made by the gut microbiome, eg Short-Chain Fatty Acids (SCFAs), such as butyric acid, propionic acid, and acetic acid, are able to stimulate sympathetic nerves, mucosal serotonin release, and to influence memory and the learning process.
Vagal nerve activity and faecal microbiota transplants are being investigated as possible interventions to influence mental health. The gut microbiome plays a facilitating role between the stress response, inflammation and depression, and anxiety.
Intestinal permeability (ie leaky gut) may occur with chronic low-grade inflammation, which happens more often in disorders such as anxiety or depression.
It is estimated that 90 percent of the body’s serotonin is made in the digestive tract (although this can’t cross the blood-brain barrier.) In fact, altered levels of gut serotonin have been linked to diseases such as irritable bowel syndrome, cardiovascular disease, and osteoporosis.
Stress can affect the composition of, and the total amount of, biome in a person’s gut. The biome can be directly affected by neurons, immune cells, and enterochromaffin cells. Enterochromaffin cells are located throughout entire gastrointestinal tract from the stomach to the rectum. They primarily release serotonin (5-HT). Enterochromaffin-like (ECL) cells in the stomach aid in the production of gastric acid through the release of histamine.
The brain also modulates gut functions such as: motility; the secretion of acid, bicarbonates, and mucus; intestinal fluid handling; and mucosal immune response. These maintain the mucus layer and biofilm where individual groups of bacteria grow.
Plus, the brain may affect the biome composition and function by changing intestinal permeability, allowing bacterial antigens to penetrate the epithelium and stimulate an immune response in the mucosa (mucous membrane). So, through the autonomic nervous system, the brain modulates immune function, which can increase epithelial permeability to bacteria, which facilitates their access to immune cells.
Changes in the composition of the gut flora due to diet, drugs, or disease correlate with changes in levels of circulating cytokines, some of which can affect brain function. Cytokines are small proteins that affect the behaviour of cells around them. They are especially important in the immune system.
Dysbiosis describes an imbalance in the gut microbiome, which can lead to an overgrowth of opportunistic gastrointestinal microorganisms, a reduction in the production of short-chain fatty acids, and reduced resistance to intestinal pathogens. The depletion of beneficial bacteria that occurs during dysbiosis is also understood to impair the immune system and trigger inflammatory disorders such as inflammatory bowel disease.
Lastly on this, the gut has its own nervous system – called the enteric nervous system.
The vagus nerve wanders round the body and contains nerves sending messages from the brain, and nerves sending messages to the brain. It affects how the gut behaves (trying to keep everything well – a homeostatic role), but it’s also part of the gut-brain axis, sending messages from the gut to the brain, which then impact on mood.
Most of the body’s immune system works on the gut! When our immune system identifies an invader, it releases cytokines, and the body is protected by inflammation as white cells attack the invading organisms. However, some people have low levels of inflammation all the time.
It’s worth noting that the brain and the immune system have two-way links.
Stress can cause inflammation. Stressful events include bereavement, poverty, debt, social isolation, maltreatment as a child. Being overweight causes inflammation. Even public speaking can increase inflammation!
Most inflammation occurs on the inside of the body, which people can’t see. One of the ways that the body naturally keeps the levels of inflammation down is through the vagus nerve. It controls the inflammatory reflex.
The inflammatory reflex is a neural circuit that regulates the immune response to injury and invasion. If cytokine levels in the body rise, the vagus nerve will detect the change and send a message to the brain. A signal is then sent down the vagus nerve to the spleen, acting on macrophages (white blood cells) to reduce the cytokine level. Cytokines can cause collateral damage to the body’s cells near them. Interestingly, vagal nerve stimulation can reduce inflammation. Increased vagal signalling inhibits inflammation and prevents organ damage.
The health and fitness of the vagus nerve is called vagal tone. A high vagal tone equates to a better capacity to keep inflammation down.
Other factors associated with increased inflammation include: obesity; sedentary lifestyle; disordered sleep; emotional and physical trauma; medical illnesses such as cardiovascular disease, diabetes, cancer, and autoimmune; infections (including exposure to unsanitary living conditions and poor hygiene); medical treatment such as surgery, chemotherapy, or radiation; and antidepressant treatment resistance.
The body’s natural immune response can trigger oxidative stress temporarily. This type of oxidative stress causes mild inflammation that goes away after the immune system fights off an infection or repairs an injury. Oxidative stress refers to an imbalance of free radicals and antioxidants in the body, which can lead to cell and tissue damage. Free radicals are molecules with one or more unpaired electron that are very reactive. Antioxidants are substances that neutralize or remove free radicals by, for example, donating an electron. The neutralizing effect of antioxidants helps protect the body from oxidative stress. Examples of antioxidants include vitamins A, C, and E.
There’s lots of research evidence linking inflammation with depression.
The blood-brain barrier protects the brain. We used to think it was impenetrable.
The neuroimmune system is composed primarily of glial cells and mast cells (a type of white blood cell). During a neuroimmune response, cytokines send inflammatory signals across the blood-brain barrier, which activates microglial cells in the brain, which then release more cytokines. As a consequence, this can cause altered plasticity, impaired neurogenesis, synaptic pruning changes, and network dysregulation. Tryptophan is a serotonin precursor. Microglial cells can instruct nerve cells to make other end products such as kynurenine. This makes less serotonin available in the brain and kynurenine (and other alternative end products) are toxic. So, inflammation in the body can have a negative impact on the brain – perhaps, leading to depression.
What else can affect a person? Well, there’s sleep, exercise, and nutrition.
But what happens if you don’t get enough sleep? Insomnia:
Is linked with depression and anxiety
Makes you forgetful
Impairs your judgement
Cognitively impairs your thinking
Causes accidents, eg falling asleep at the wheel
Is linked to health issues (heart attack, stroke, diabetes)
Kills sex drive
Ages your skin
Can cause weight gain
Increases the risk of death.
If you do get enough sleep, it:
Reduces stress
Reduces the risk of depression
Makes you more alert
Improves your memory
Cleans up your brain
Makes you cleverer
Helps your body repair itself
Reduces inflammation
Keeps your heart healthy
May prevent cancer
May help you lose weight.
Research shows there are links between insomnia and anxiety.
The benefits of exercise (movement) are that it:
Creates new brain cells (neurogenesis) using BDNF (brain-derived neurotrophic factor).
Improves your mental health and mood
Helps keep you thinking and learning
Improves your sleep
Strengthens bones and muscles
Reduces your risk of heart disease
Help you manage your blood sugar and insulin levels
Increases your chances of living longer
Improves your sexual health
Reduces the risk of some cancers.
Nutrition helps with your biome and helps your GI (gastrointestinal) tract.
Good things to eat include: all the food groups (carbohydrates, fats, proteins, vitamins, minerals, and water) in moderation, prebiotics and probiotics, anti-inflammatory foods (eg fruits, greens, nuts, and grains), and foods containing antioxidants (eg dark chocolate, whole cereal, fruit, and vegetables).
Food tips for a good mood include: eat breakfast, stay hydrated, eat regularly, eat the right kind of fats (not trans fats), and avoid processed foods.
All of these impact on your body and your brain, and therefore how you feel, think, and behave.
As you go through life, you develop your model of the world. These experiences will usually be similar but different to your friends and family and this will lead to your beliefs and your values. These will affect how you behave and how you feel about things. Of course, your memories of an experience will change every time you recall that memory.
What else can affect how we feel? If we are suffering pain, that can have a big negative impact. Our hormone levels can affect us (for example menopausal women, or if our body is flooded with adrenalin). If we tend to brood, this involves various distributed networks, such as the default mode network and the salience network, as well as brain areas such as the medial prefrontal cortex and the anterior cingulate, and that can impact on how we feel.
If we control our breathing (for example 7-11 breathing, square breathing), that can have a positive impact on how we feel. Diaphragmatic breathing with slow exhalations is associated with increased parasympathetic regulation, likely mediated partly through vagal pathways, and slows our heart rate and reduces our blood pressure.
Laughter can have a huge positive effect on how we feel.
Meditation, eg the Loving-kindness meditation can help us to feel better and then behave in a more positive way. Here’s how...
Say three times: “May I be filled with loving kindness, and be well, peaceful and at ease, happy, and free of suffering”.
Then say three times for a loved one: “May [loved one] be filled with loving kindness, and be well, peaceful and at ease, happy, and free of suffering”.
Lastly, say three times for each: a neutral person, a difficult person, and all sentient beings. May [neutral person] be filled with loving kindness, and be well, peaceful and at ease, happy, and free of suffering.”
This constitutes one cycle. You can do as many or as few cycles as you wish.
Doing things that make us happy is good, but, often, what we think will make us happy doesn’t. Hedonistic happiness includes things like eating chocolate and going to the pub every Friday. Hedonic adaptation results in us not enjoying them as much as we expected. Eudaimonic happiness (or wellbeing) refers to the subjective experiences associated with living a life of virtue in pursuit of human excellence. What that really means is experiences are usually more enjoyable than things.
Events can have a big impact on where we are on the happy-sad scale. Evidence shows that if you have a big win (or a big loss) in life, typically, after a while you are back to your original level of happiness. In fact, how we interpret events has a bigger impact than the event itself. So, it’s often estimated that 90 percent of the impact of an event is how we interpret it, and only 10 percent is the event itself.
The exact phrasing of this concept – “I am convinced that life is 10% what happens to me and 90% of how I react to it” – originates from a widely celebrated essay on ‘Attitude’ by the American pastor and author Charles R. Swindoll, however, there doesn’t seem to be any scientific research.
Pressure can impact us negatively. This is where someone (our boss) demands work is done by a particular time. This causes negative stress in our life. Too much pressure, whether real or imagined, can lead some people to thoughts of suicide.
Other people’s actions and reactions to what we say and do can not only impact on how we feel and how we behave, it can also impact on our values and beliefs. So, spend time with positive people.
NLP has a model of what goes on in a person’s head, and this affects how successful an attempt to make a change will be. Robert Dilts came up with a model of what, he called, logical levels (see Figure 2). It’s worth noting that the model is a coaching/NLP framework rather than an evidence-based psychological model.
Figure 2: NLP logical levels
At the bottom is environment. This is like the opium addicts in the Vietnam war. Changing their environment (ie going home) changed their behaviour. Above environment is behaviour, above that is capabilities – you can only do what you’re capable of doing. Above that are beliefs and values, above that is identity, which, I guess, used to be more important where someone was identified by their job, for example doctor, colonel, etc. Above that is put mission or purpose, or, sometimes, spirituality.
Other things people talk about in terms of getting themselves to do something are motivation, resilience (if other things or people are trying to stop them), and willpower (or grit when the going gets tough).
And if we want to be positive about things, then we need to have positive thoughts, positive actions, positive interactions, and a purpose to our life. If we don’t have enough of any of those, this can lead to negative emotions and thoughts.
I also want to mention mindset. People with a fixed mindset think that their positive characteristics are fixed and there’s nothing they can do about them, so they will behave in ways to hide their failures and make the most of their successes. People with a growth mindset know that they will be able to work hard and improve throughout their life. So, they will take risks with tasks because they treat failure as a learning exercise. The ideas are based on the ideas of Carol Dweck.
If you are feeling anxious, then this can lead to behaviours like OCD, fears and phobias, and panic attacks. It can make pain hurt more.
And thoughts, feelings, behaviour, and physical reactions (eg blushing) are linked, so a change in one can cause a change in the others (see Figure 3).
Figure 3: Relationship between thoughts, feelings, and behaviour
Modern neuroscience increasingly suggests that the brain is not simply reacting to the world around it. Instead, it is constantly trying to predict what is going to happen next. This idea, sometimes called predictive processing, suggests that the brain works like a prediction machine. It uses past experiences to build models of the world and then uses those models to anticipate what is likely to happen.
When incoming information matches the brain’s expectations, everything feels smooth and familiar. But when something unexpected happens, the brain experiences what neuroscientists call a prediction error. The brain must then decide whether to update its model of the world or interpret the new information in a way that fits what it already believes.
This can help explain why some people become anxious. If a person’s brain has learned to predict danger, criticism, or failure, it will scan for evidence that confirms those expectations. Neutral situations may then feel threatening, even when no objective threat exists. This is one reason why changing expectations and building positive experiences can be so powerful in therapy. The brain gradually updates its predictions and starts to expect safer and more positive outcomes.
Much of what we do is learned through experience. Psychologists describe this through learning theory.
Sometimes we learn by association. If someone has a frightening experience while giving a presentation, their brain may begin to associate public speaking with danger. This is called classical conditioning. The next time they stand to speak, anxiety appears automatically.
We also learn through consequences. Behaviours that bring relief or reward are likely to be repeated. This is called operant conditioning. For example, someone with social anxiety may avoid social events and feel immediate relief. That relief rewards avoidance, making it more likely they will avoid similar situations in future.
This helps explain why habits, phobias, compulsions, and avoidance patterns can become deeply ingrained. The brain is always learning what seems to keep us safe. Therapy often works by helping clients create new learning experiences, allowing old associations to weaken and healthier responses to develop.
Our earliest relationships shape how we understand ourselves and others. Attachment theory suggests that the bond between a child and their caregivers helps build internal expectations about relationships and safety.
When caregivers are reliably warm and responsive, children often develop secure attachment. They learn that people can be trusted and that they themselves are worthy of care and support.
When care is inconsistent, rejecting, or frightening, children may develop insecure attachment patterns. These can lead to expectations of abandonment, criticism, unpredictability, or emotional distance. These expectations often continue into adulthood, affecting relationships, self-esteem, stress regulation, and emotional resilience.
These patterns are not fixed for life. New experiences, supportive relationships, and therapeutic work can help people develop greater security and flexibility.
Humans are social creatures, and our social environment has a powerful influence on how we think, feel, and behave.
Factors such as loneliness, poverty, inequality, discrimination, social exclusion, and chronic uncertainty can place the nervous system under prolonged stress. When the brain repeatedly detects social threat, it can become more vigilant and reactive. This may contribute to anxiety, low mood, irritability, poor sleep, and difficulty concentrating.
On the other hand, belonging, social support, acceptance, and connection help regulate the nervous system. Positive relationships buffer stress, reduce inflammation, improve resilience, and promote wellbeing.
This is one reason why spending time with supportive, positive people can have such a powerful impact on mental health.
For many years, emotions were thought to be automatic reactions generated by specific parts of the brain. More recent research, particularly the work of Lisa Feldman Barrett, suggests something more complex.
Constructed emotion theory proposes that emotions are actively created by the brain rather than simply triggered. The brain constantly combines sensory information from the outside world with signals from inside the body – such as heart rate, breathing, muscle tension, and energy levels. This internal information is called ‘interoception’.
The brain then uses past experience and context to make sense of these sensations and construct an emotional experience.
For example, a racing heart could be interpreted as excitement before giving a presentation or as fear and panic. The physical sensations may be very similar, but the brain’s interpretation determines the emotion experienced.
This means emotions are not fixed reactions that happen to us. They are active constructions shaped by prediction, learning, context, and interpretation. This gives us greater potential to influence how we feel by changing how we understand our internal experiences.
These ideas help us see that human behaviour is not random and rarely caused by one single factor. It emerges from an ongoing interaction between biology, learning, relationships, social context, bodily state, and the brain’s continual attempt to predict and make sense of the world.
Anyway, that’s a very quick run through the different factors affecting why people do what they do, and that’s without even looking at the things we already know about the brain.