You are going to spend a lot of the next 24 hours reading all kinds of reasons why the Phillies will enter Friday’s World Series opener as a heavy underdog against the Astros. Those reasons are more than valid. But this year’s postseason is a perfect example of how little anyone really knows. We saw it with the Giants in 2010 and the Cardinals in 2011: a best-of-seven series is a wildly different environment than a 162-game season. A playoff football game is 1/17th of an NFL regular season. A playoff NBA series is 1/12th. A seven-game baseball series is 1/23rd of a baseball regular season. Any…