Net gains: What a tennis great can tell us about equity investing

Imagine you're a tennis player with hopes of carving out a career on the professional circuit. You make your debut at the age of 17, and during the next quarter-century or so, over the course of hundreds of matches, you manage to win a shade above 50% of all the points you contest.  While it may not sound earth-shattering, this ratio obviously amounts to a winning record of sorts. But how would it translate into actual achievements? Might you sneak through the first few rounds of a tournament from time to time? Would you pull off an occasional major upset? Could you even make a living? ...