What would make a celebrity like Tiger Woods -- who's reportedly getting help for his sex addiction in rehab -- risk it all just for some sex on the side? Being an adrenaline junkie is part of the issue, says psychologist Doug Hirschhorn, PhD., author of Eight Ways to Great: Peak Performance on the Job and in Your Life. "Tiger's been raised all his life to be an intense competitor," says Hirschhorn, who hasn't worked directly with the athlete or any of the celeb cheaters in this gallery. "But he’s been at the top of his game for so long that, if he’s lucky, he gets maybe one good rush during the course of a tournament." But there's hope for him, says Hirschhorn: "I think things spun way out of control and Tiger probably felt relief that he was forced to stop."