The secret of happiness may be to not expect too much from life.
For if you start off with low expectations you could end up pleasantly surprised, according to a scientific study into human happiness.
British scientists found that day-to-day wellbeing does not reflect how well things are going, but whether things are going better than expected.
Dr Robb Rutledge of University College London said his team were surprised to find just how important expectation is.
He said: ‘It is often said that you will be happier if your expectations are lower. 
‘We find that there is some truth to this - lower expectations make it more likely that an outcome will exceed those expectations and have a positive impact on happiness.’
But his team of researchers, who tested their theory on 18,000 people, also discovered a converse force affects our mood.
While low expectations can make us happy if they are exceeded later, having high expectations to begin with make us happy earlier.
Dr Rutledge said: ‘Expectations also affect happiness even before we learn the outcome of a decision. 
‘If you have plans to meet a friend at your favourite restaurant, those positive expectations may increase your happiness as soon as you make the plan.’
His team combined the contrasting aspects of expectation and its impact on happiness and wrote it into an equation, which they discovered accurately predicted people’s happiness.
The equation accurately predicts how happy people will say they are based on recent events.
The formula, published in the Proceedings of the National Academy of Sciences, was put together by studying 26 people who completed a decision-making task in which their choices led to monetary gains and losses.
They were repeatedly asked how happy they were, and their brain activity was measured using MRI scans.
The scientists used the data to build a computer model, which was tested on 18,420 people using a smartphone app.
The results confirmed that people who started off with lower expectations were happier when they had better results.
The authors wrote: ‘Conscious emotional feelings, such as momentary happiness, are core to the ebb and flow of human mental experience.
‘Our computational model suggests momentary happiness is a state that reflects not how well things are going but instead whether things are going better than expected. 
‘This includes positive and negative expectations, even in the absence of outcomes.’