“Happiness is not about how well you’re doing in general, but rather if you’re doing better than expected,” said study author and neuroscientist Robb Rutledge of the Max Planck UCL Centre for Computational Psychiatry and Ageing.

For instance, say you go to a restaurant where the food was the best you’ve ever had. According to the happiness equation, you would actually be happier at the end of the meal if you had expected it to be just average, as opposed to assuming it would be as delicious as it was.

“Most of our senses are much more tuned to changes in things than to levels, and the same is true for happiness,” said economist George Loewenstein at Carnegie Mellon University, who was not involved in the study. “This ensures that however successful we are, we are always going to be driving for more.”

But this doesn’t mean that having low expectations is the path to happiness, because the model also shows that such pessimism leads to discontentment while you wait for an outcome.