Great article (PDF format) from Michael Maboussin:
Can be downloaded from this link:Outcomes from many activities—including sports, business, and investing—are the combination of skill and luck. Most people recognize that skill and luck play a role in results, yet they have a poor sense of the relative contribution of each. The ability to properly untangle skill and luck leads to much better thinking about most day-to-day outcomes, and allows for sharply improved decision making.
Untangling Skill and Luck