What Is Optimism Bias? | Definition & Examples

Optimism bias is the tendency to overestimate the likelihood of positive events and underestimate the likelihood of negative events. Optimism bias causes most people to expect that things will work out well, even if rationality suggests that problems are inevitable in life.

Example: Optimism bias
You’ve just bought a new bike, and the salesperson asks you whether you also want to look for a helmet.

Because you’ve been riding a bike since you were young, you think the chances of getting involved in an accident are really small. You conclude that you’ll be fine without it. Optimism bias makes you underestimate the risk of riding a bike without a helmet.

Although optimism bias can motivate us to overcome obstacles, it can also cause us to ignore potential risks, resulting in poor decision-making.

What is optimism bias?

Optimism bias (or unrealistic optimism) is a type of unconscious cognitive bias. It refers to an unrealistically favorable attitude that people have towards themselves and people that are close to them. Positive illusions help us maintain self-esteem and avoid discomfort, at least in the short term.

Optimism bias causes people to believe that they are less likely to experience negative events than other people. For example, people expect that their careers, marriages, or health will be better than those of others, and that the financial troubles, divorces, or illnesses that happen to other people will not happen to them.

Optimism bias

This irrational belief seems to be deeply ingrained in humans. Studies suggest that it is observed in about 80% of the population (but, notably, not among people with depression).

Why does optimism bias occur?

Maintaining a positive outlook gives us courage and motivates us to keep going, despite any adverse situations we face. Optimism bias allows us to try new or difficult things because we feel confident that they will go well.

Throughout human evolution this characteristic served us well and was passed down from one generation to the next. In other words, because optimism bias proved beneficial to humans, we are inclined to mispredict the future.

There are two key assumptions at the root of optimism bias:

  1. That we exercise some level of control over the world around us, including what will happen to us in the future.
  2. That we, as individuals, possess more positive traits than the average person.

Several factors can help explain optimism bias:

  • We have the tendency to selectively update our beliefs and expectations about the future. We are more likely to update our beliefs based on positive information rather than negative information. This, in turn, perpetuates optimism bias.
  • Optimism is beneficial to our mental and physical health. Expecting positive outcomes reduces stress and anxiety. Optimistic patients are more likely to believe that they will recover, leading them to adopt behaviors that increase their chances (e.g., exercise, healthy diet).

Overall, optimism bias enables us to cope with our environment and worry less about uncertainty. Because of this, it can often lead to better results than unbiased or rational beliefs.

Why does optimism bias matter?

Because a majority of people are susceptible to optimism bias, it’s important to be aware of its influence on our perception and judgment.

Optimism bias can be a problem when it prevents us from accurately anticipating risk. In project management, for instance, optimism bias can cause us to underestimate the budget and time needed, a common error called the planning fallacy. Failure to assess potential hazards can also mean failing to take out sufficient insurance or to get regular medical check-ups. It can even cause us to adopt harmful habits, such as smoking.

On the other hand, optimism is also linked to achievement in several domains, such as sports, business, and education. When we are optimistic, we are more motivated to try harder, which in turn can influence the outcome. Sometimes, expecting positive things can become a self-fulfilling prophecy.

Optimism bias examples

Optimism bias can also influence collective behavior and produce large-scale effects.

Example: Optimism bias and the economy
Several experts consider optimism bias to be one of the core causes of the financial crisis of 2007-2008. Individuals, analysts, and government officials were all too optimistic that the economy would grow (i.e., that businesses would continue to be profitable, that there would be more jobs for people, and that incomes would increase), leading them to ignore any warning signs.

This shows that when many people hold unrealistic expectations, their bias accumulates and is amplified, producing large scale effects.

Optimism bias can have negative consequences, particularly when serious risks are disregarded.

Example: Optimism bias and climate change
Some argue that optimism bias may help explain why we don’t do anything about climate change, even though we acknowledge the threat. Studies have shown that people who are more optimistic about a range of possible future events (e.g., contracting an illness, World War III) are also less concerned about the environment.

This also seems to extend to feeling that they are safer than others living elsewhere or future generations. This leads them to believe that climate change won’t personally affect them.

Additionally, among climate skeptics in particular, more optimism is associated with less guilt, less perceived responsibility, and lower behavioral intentions. Thus, overall, optimism seems to be negatively associated with an active response to environmental change.

How to avoid optimism bias

Although optimism bias is part of human nature (and can’t be entirely avoided), there are ways to keep it in check:

  • Perform a project “premortem.” A premortem analysis starts with the hypothesis that your project has failed. With that in mind, you try to come up with possible reasons why. This allows you to spot the weaknesses in your project plan and prepare for the future.
  • Use the availability heuristic. Actively attempt to retrieve negative past experiences or times things didn’t go as planned. Here, the purpose is not to demotivate yourself, but to learn from the past so as to make sensible choices in the future.
  • Take an outsider’s approach. Take an objective approach when making plans. For example, when you estimate how long you will need to write a paper, seek out information about the average time it takes most people and adjust your initial assumptions accordingly.

Other types of research bias

Frequently asked questions about optimism bias

What is the opposite of optimism bias?

The opposite of optimism bias is pessimism bias. Optimism bias occurs when we overestimate our chances of experiencing positive events in our lives, while pessimism bias occurs when we overestimate our chance of experiencing negative events.

For example, pessimism bias could cause someone to think they are going to fail an exam, even though they are well prepared and get good grades.

What is a positive illusion?

A positive illusion is a form of self-deception under which people have inflated, favorable attitudes about themselves or others close to them.

The most common positive illusions involve:

  • Exaggerating one’s positive traits
  • Overestimating one’s degree of control in life
  • Harboring overly optimistic beliefs about future events (also called optimism bias or positivity bias).
What is the planning fallacy?

The planning fallacy refers to people’s tendency to underestimate the resources needed to complete a future task, despite knowing that previous tasks have also taken longer than planned.

For example, people generally tend to underestimate the cost and time needed for construction projects. The planning fallacy occurs due to people’s tendency to overestimate the chances that positive events, such as a shortened timeline, will happen to them. This phenomenon is called optimism bias or positivity bias.

What is a self-fulfilling prophecy?

A self-fulfilling prophecy is a belief about a future event that leads people to act a certain way, ultimately bringing about the expected outcome. In other words, we cause something to happen just because we expect it.

This suggests that beliefs have the power to alter people’s behaviour in such a way that they become a new reality in the end. Optimism bias can create a self-fulfilling prophecy: when we expect positive things, we are more likely to align our actions with this belief and try harder to influence the outcome.

What is positivity bias?

Positivity bias is phenomenon that occurs when a person judges individual members of a group positively, even when they have negative impressions or judgments of the group as a whole. Positivity bias is closely related to optimism bias, or the expectation that things will work out well, even if rationality suggests that problems are inevitable in life.

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Nikolopoulou, K. (2023, October 05). What Is Optimism Bias? | Definition & Examples. Scribbr. Retrieved 22 February 2024, from https://www.scribbr.co.uk/bias-in-research/the-optimism-bias/

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Kassiani Nikolopoulou

Kassiani has an academic background in Communication, Bioeconomy and Circular Economy. As a former journalist she enjoys turning complex scientific information into easily accessible articles to help students. She specialises in writing about research methods and research bias.