Quoted from http://scienceblogs.com/cortex/2010/04/the_superstar_effect.php

via scienceblogs.com/

According to a paper by Jennifer Brown, an applied macroeconomist at the Kellogg School of Management at Northwestern University, Mr. Woods is such a dominating golfer that his presence in a tournament can make everyone else play significantly worse. Because his competitors expect him to win, they end up losing; success becomes a self-fulfilling prophecy.