He abstained from sex for five years when he was an up-and-comer because he believed that having sex before a fight made him a weak boxer.
For the record, Iron Mike isn't the first boxer to subscribe to the "no sex before a big fight" theory. Everyone from Manny Pacquiao to Amir Khan has also admitted to toning things down in the bedroom in the months leading up to a fight. But most boxers don't take it to the level that Tyson did at the start of his career. Don't worry, though. According to him, he's more than made up for missing out on those five years since then.