"Competition against daunting opponents makes your own performance worse."

A study by Northwestern University appearing in the Journal of Political Economy investigated 11 years of Tiger Woods' records against various PGA opponents, and found that the simple fact that they were facing Woods made them worse golfers. His opponents tended to play more conservatively when competing directly against him, taking shorter, safer shots. The economist Jennifer Brown estimates that the influence of this effect made Woods an extra $6 million overall.