He now joins the legions of other sports figures whose careers have imploded over allegations of illegal steroid use. In recent days, for example, two Major League Baseball players, including San Francisco Giants star Melky Cabrera, were banned for 50 games without pay for using performance-enhancing drugs. The outsized ambition that drives athletes to reach the very highest levels of achievement too often is also the cause of their downfall. In their constant search for anything that might give them an edge over the competition they may even feel justified in taking ethical shortcuts and reckless risks with their bodies in order to win, on the assumption that everyone else is doing the same. But sooner or later their actions come back to haunt them.