**Hedonic adaptation** is the idea that humans get used to good and bad events over time. 

Good and bad events change happiness in the moment, but people get used to them. This is called adaptation. Because of adaptation, happiness usually stays the same over time. 

Hedonic adaptation is also called the **hedonic treadmill**. Looking for good events will only make a person adapt to them, leading them to want more.

Origins
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Hedonic adaption was developed in 1971.  Scientists found that lottery winners were not happier than those who did not win. Also, those who could not walk were not much less happy than those who could. 

Newer studies show the same. For example, a 15-year-long study shows that married people in Germany were much more happy after marriage, but only for a short period of time. By the second year, their happiness was the same as before they got married. 

These studies show that it may not be possible to increase happiness for a long period of time.

Mechanisms
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Hedonic adaptation contains two important ideas. First, how people feel about an event depends on how they feel before it happened.  This means that good events make people happy in the moment. But over time, because they are already happy, their happiness does not change. Second, happiness usually returns to a point that stays the same.  This is how people get used to events over time. 

Scientists thought that happiness returns to a neutral point: where a person is not happy nor sad.  However, new studies show that most people are happy most of the time.  So, happiness returns to a point where the person is happy. This point is different for everyone. How happy a person is may depend on personality: how a person usually acts and feels. This can come from their parents. 

Hedonic adaptation comes from cognitive changes: changes in how a person thinks.  These changes are what a person likes and wants, and what they do and do not think about. Thinking about an event less is the main way adaptation happens. 

Hedonic adaptation also comes from neurochemical changes: changes in the brain that make good and bad feelings less strong. 

However, people do not get used to all events. Most studies show that people usually adapt to good events quickly and completely.  Their happiness returns to exactly where it was before the event soon after the it happens. However, some strong or long-lasting bad events, such as losing a job or partner, result in less adaptation.  Happiness may not completely return to its point before the event. In some situations, it may decrease.

Functions
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### Protection

From an evolutionary position, hedonic adaptation is useful. It helps control the effects of bad events. It makes bad events less strong. This protects people from difficult situations and helps them survive in the present. 

Some effects of bad events are helpful.  They tell us what is important. For example, hunger, thirst and pain. Other effects can be dangerous.  Long periods of fear and worry for example, can harm the body and the mind, leading to disease and illness. 

Hedonic adaptation is a part of the "psychological immune system". It protects people from dangers to their health. This often happens unconsciously, without the person knowing. 

### Perception

Hedonic adaptation can change the way people see their situation.  As bad events become less strong, people are more likely to make changes to better the situation. 

For example, the death of a partner can make people very sad. They see no way to make the situation better. However, adaptation helps people see what can be changed. They may try to prevent a similar event from happening. This helps people learn from past events to survive in the present.

Applications
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### Treadmill effect

Good events make people happy in the moment. But not for long. People look for other things to stay happy. People get used to them too. This treadmill effect means that the more a person gets, the more they want. This makes staying happy hard. 

### Quality of decision-making

A person who is not used to an event often thinks it is more important than it really is.  For example, healthy people think unhealthy people are less happy than they really are.  People who are not used an event can think jobs, marriage, and where they live will affect their happiness more than it really will. 

### Moral values

Being used to an event may change what people think is right and wrong.  For example, people in the Milgram experiment were asked to harm another person multiple times. Each time was more harmful than the last. When people become used to harming others, they may no longer think that it is wrong. 

### Prevention

There are ways to prevent hedonic adaptation. For example, the Hedonic Adaptation Prevention Model (HAP) says that variety and appreciation can make happiness last. 

Variety is when happiness comes at a surprise even after the event has happened.  The surprise makes getting used to the event difficult. This keeps happiness high. It also stops people from wanting more. 

Appreciation is when a person is happy with what they have.  They know that they may lose it. This is the opposite of adaptation. By being appreciative, people are reminded of the good event. Thinking about it makes happiness continue. 

Giving something up and getting it back can also prevent hedonic adaptation and make happiness last.

Critical views
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### Areas of Happiness

Hedonic adaptation says that happiness returns to a single point. However, happiness comes from many things. Change in one area of happiness, such as at work, does not always mean change in another area of happiness, such as in marriage. Different areas of happiness can change in different ways and at different times.  The point where happiness returns to after an event may be different depending on which area of happiness is affected. 

### Happiness can Change

Hedonic adaptation says it may not be possible to increase happiness for a long period of time. People will always get used to good events. However, a 17-year-long study found that 24% of people said their happiness changed a lot between the first and last five years. 

Another study found that differences in happiness can be explained by how much freedom or money countries have.  They last for a long time. The difference in happiness shows that people do not completely adapt to some events. For example, a study shows that people adapt to money, but not status: how others see them.