“I know a man who gave up smoking, drinking, sex and rich food. He was healthy right up to the day he killed himself.”

This old wisecrack is credited to American late-night talk show host and comedian Johnny Carson. Sorry, Johnny, it may be funny, but you’ve got it wrong. Although giving up unhealthy habits like smoking, drinking and rich food will certainly improve your health, giving up sex will not.

One of the biggest reasons that it’s so hard for facts to change people’s minds is that people have an incentive to keep believing what they already believe, especially if it’s a belief that’s deeply tied to their identity.

The mental gymnastics they do to achieve this are known in psychology as “motivated reasoning.” It’s something that’s extremely hard to get around.