Optimism vs pessimism: which side is science on?

Despite Monty Python’s musical suggestion that we “always look on the bright side of life”, humans have evolved to be capable of both optimism and pessimism. Some people are always thinking the best, some the worst, and the rest of us sit on a spectrum in between the two. But why are these two perceptions such fundamental traits of our brains? What are the evolutionary advantages of optimism and pessimism, and how do these two perceptions affect our thinking and our attitudes to the world?

Broadly speaking, nobody is completely optimistic or pessimistic – indeed, a complete absence of one of these traits actually carries some negative connotations. Zero optimism is often seen in people with very severe cases of mental illnesses such as depression or anxiety, while a total lack of pessimism is associated with unrealistic expectations about yourself and others (leading to victim-blaming in situations and harmful suppression of your emotions). Generally, researchers have found that most people sit between these two extreme poles, and that their attitudes can shift in response to events and external stimuli.

Both optimism and pessimism are useful traits that affect how we perceive the past, present, and future. According to something known as the ‘fading affect bias’, memories for negative emotional experiences are forgotten faster than positive ones, thus infusing our past with happier memories. However, researchers have established that our emotion and attention systems show a negativity bias. So, while we may lose negative memories faster, we also spend more time thinking about them.

Optimists have better mental health, and they may actually live longer

Similarly, the ‘planning fallacy’ sees our brains always tend towards the positive – when we approach a task, familiar or not, we generally underestimate how long it will take to complete, showing an inherent optimism. Yet our brain is also very good at coming up with worst-case scenarios and dangers, even in the most mundane of places. It’s a joint partnership – optimism provides motivation and compels us to keep going, while pessimism offers a bit of grounding and keeps us wary of risks.

According to studies, on average, people tend to be more optimistic than pessimistic. Psychologists find that optimism is relatively stable and consistent over time, although some research has discovered that a minority of people become more or less optimistic as time passes. Although these are a few exceptions, most studies of optimism have shown that being more optimistic is actually good for you too – optimists have better mental health, and they may actually live longer.

In studies of students, those who were more optimistic at the beginning of a term reported feeling less distressed at its end. This has been connected to a style of coping known as approach coping, or engaging with a problem – pessimists opt for avoidance coping, denying or disengaging with a problem, which has been found to be less effective. Long-term outcomes for optimists suggest they are less likely to drop out of university, and to have a higher income later in life.

Optimism may be difficult for anxious people, and thus defensive pessimism is an alternative approach for dealing with anxiety

There are also physical benefits to tending towards optimism, not least the production of the neurotransmitter dopamine, which makes us feel happier. A 2019 study found that optimists reported higher sleep quality despite resting for similar timespans to pessimists, while other research has linked it to reduced risk of a heart attack and lower risk of high blood pressure. Strikingly, recent research suggests that optimism could extend your lifespan by as much as eight years.

I don’t want to completely rule out pessimism, though, and the psychologist Julie Norem has identified one key benefit. Defensive pessimism, in which people cope with anxiety by imagining the possible negative outcomes of a situation, might be useful, because you can use it to anticipate and prepare for negative events. Norem suggests optimism may be difficult for anxious people, and thus defensive pessimism is an alternative approach for dealing with anxiety (presuming it’s focused on things you can actually do something about): “There’s no right way to think about things that fits every situation and every person. You have to find ways of working in the world that fits for you.”

If you’re curious about your own levels of optimism and pessimism, you should check out the Life Orientation Test – it’s what researchers use to measure these two traits, and simply involves you agreeing or disagreeing with some statements. Ultimately, though, whether you’re seeing that glass as half-full or half-empty one day, both answers are useful ones – it just means your brain has a particular focus on one set of priorities.