We all plan for the future, whether it’s a large construction project or a small job around the house. But why do they always take longer and cost more than you expected?

Ever packed your bag before you leave work with papers with the plan that you would do some more work at home overnight and then, more often than not, gone back to work the next day with all of it untouched? Is it your failings or something deeper?

There are many examples of being overly optimistic: the estimations in 1957 for the Sydney Opera House was that it would be completed in 1963 for $7 million. A scaled down version was opened in 1973 at a cost of $102 million.

This phenomenon intrigued Professor of Psychology, Roger Buehler and his colleagues and so they decided to carry out some research.

They surveyed university honours students who were working on their thesis projects, asking them to predict when they would finish their thesis. The students, on average, estimated it would take 33.9 days to complete. It actually took the students 55.5 days. That’s an increase of 64%!

Other studies amongst stockbrokers, electrical engineers and doctors found similar results.

So why is there such a gap between intention and behaviour?

Buehler explains it as there are two types of thinking – an inside approach and an outside approach. An inside approach focuses on the case at hand, like you are developing a mental simulation on how a project will unfold. The problem is that these simulations are often oversimplified or idealised and don’t consider alternate ways that things may go. In other words, you are planning to succeed not planning to fail.

This approach of seeing the future through rose coloured glasses is termed ‘Optimism Bias’.

Cognitive Neuroscientist Tali Sharot from the University College London says that the brain tends to process positive information more readily than negative information. Also, people with a pessimistic bias tend to be slightly depressed. Hence positivity is a good thing, it drives us forward. It motivates. If you expect positive things then stress and anxiety is reduced.

Optimism bias may well be an evolutionary trait. By believing that an outcome will be positive, you are more likely to take action. It may well have played a role in some of the astounding progress that humankind has made over millennia – space travel, cures for diseases, technological advances.

Someone had to dream the dream and then have the belief that it was possible. The lesson is to keep positive and keep pushing yourself.