Based on probability, assuming the two teams are equal, the team leading 2-0 should win the World Series 81% of the time. However, given that one of the teams won the first two games, maybe the two teams aren't equal. You could easily speculate that the team leading is the better team. You would then expect that team to win more than 81% of the time.

What does history tell us?

A team has gone up 2-0 in a seven-game World Series 47 times. Based on the 81% you would expect 38 World Series Championships from the 47 teams. The actual number is 37. Close enough. But it does call into question the speculation that the team leading 2-0 is the better team. The assumption that the two teams are equal, despite one of them leading 2-0, is probably a good one.

What about more recent history?

If you limit the time frame to the last 50 years, you find that the team down 0-2 comes back much more often than probability would suggest. It's happened 10 times in those fifty years, while the team leading 2-0 has won 17 times. That's only a 63% winning percentage.

The moral of the story: If you're a White Sox fan, don't get over-confident.