Although we are taught the benefits of kindness and altruism, it seems we are happiest when simply told to pursue our own self-interest.
Researchers found the key to contentment is feeling we have no choice but to be selfish.
In contrast, the study, carried out by psychologists at the University of Pennsylvania, found that those who actively choose a selfish path usually have to battle with guilt.
They speculated that because we're taught as children that 'sharing means caring', if we make a decision out of self-interest, we often feel bad for prioritising ourselves over others.
But that frequently means we forego the things we know will make us happy.
Psychological scientists Jonathan Berman and Deborah Small of the University of Pennsylvania carried out tests to see when people feel happiest.
In one they recruited 216 undergraduates and gave them each 3 dollars.
Some were told to donate it to the charity UNICEF, some were told to keep the money and some participants were told that they could choose what to do with it.
Those students told to keep the money for themselves reported being far happier with the outcome than those who were told to donate the money and those who were free to choose.
Mr Berman said: Often what people really want to do is act in a selfish manner.
But they don't do that, because they know they would feel selfish if they did.
The research is published in Psychological Science, a journal of the Association for Psychological Science.
