The winner effect is a term used in biology to describe how an animal that has won a few fights against weak opponents is much more likely to win later bouts against stronger contenders. As Ian Robertson reveals, it applies to humans, too. Success changes the chemistry of the brain, making you more focused, smarter, more confident and more aggressive. And the more you win, the more you will go on to win. But the downside is that winning can become physically addictive.