Optimism and pessimism are fundamental traits of the human brain. With optimism, there’s the ‘Just World’ hypothesis, an ingrained assumption that the world is fair and that good actions will lead to good outcomes, and vice versa for bad ones.

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There’s also the ‘fading affect bias’, where memories for negative emotional experiences fade faster than positive ones. And then there’s the ‘planning fallacy’, a cognitive quirk where we constantly underestimate how long a task (such as driving to the airport) will take, regardless of how often we’ve done it before.

These three traits alone show that optimism infuses our perception of past, present, and future. The same goes for pessimism, however. While our memories may skew positive, our emotion and attention systems show a negativity bias – we give more weight to and spend more time dwelling on negative experiences. And while the human brain has the impressive ability to create complex simulations of events and scenarios, much of this is used for negative or worst-case scenarios, and taboo thinking.

Ever stood on a cliff or high building and thought “What if I jump?” for no discernible reason? Now you know why. This is how our brain works. We need optimism to keep us motivated, to compel us to perform actions, and reassure us that we have control over our own lives. And we need pessimism to keep us grounded, wary of risks and dangers, to make us recognise limits and restrictions.

A complete absence of optimism is often seen in people with severe cases of depression and anxiety, while zero pessimism can lead to unrealistic expectations, victim-blaming and harmful emotional suppression.

Exactly which is more important in any given situation will vary considerably, but it’s impossible to deny that both optimism and pessimism are essential parts of our psyche.

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Every week on BBC World Service, CrowdScience answers listeners’ questions on life, Earth and the Universe. Tune in every Friday evening on BBC World Service, or catch up online at bbcworldservice.com/crowdscience

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Authors

Dean is a neuroscientist, author, blogger, occasional comedian and all-round ‘science guy’. He is the author of the the popular Guardian Science blog ‘Brain Flapping’ (now ‘Brain Yapping’ on the Cosmic Shambles Network with accompanying podcast), the bestselling books The Idiot Brain and The Happy Brain, and his first book aimed at teens, Why Your Parents Are Driving You Up the Wall and What To Do About It.

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