We often assume we see our physical surroundings as they actually are. But new research suggests that how we see the world depends on what we want from it.

People see desirable objects as physically closer than less desirable ones, according to a study in the January issue of Psychological Science. When psychologists Emily Balcetis of New
York University and David Dunning of Cornell University asked people to estimate how far away a bottle of water was, those who were thirsty guessed it was closer than nonthirsty people did. This difference in perception showed up in a physical challenge, too. People tossing a beanbag at a $25 gift card were, on average, nine inches shy, whereas people aiming for a gift card worth nothing overshot by an inch.

As the brain evolved, people who saw distances to goals as shorter might have gone after what they wanted more often. This error in perception was actually an advantage, leading people to get what they needed—and, perhaps, survive more often than their more accurate counterparts. “Seeing water as closer when you’re thirsty might make it a little more likely you’ll try to go get it,” Balcetis says.