Over 11 years ago, I wrote about Magic Numbers. Trust me, there's nothing supernatural about this magic. Here's an excerpt of what I wrote back then.
My fondest memories are of the Magic Number. The Magic Number is simply the number of games that the team leading a division needs to win to ensure winning the division. If you're leading the division with ten games remaining and your Magic Number is three, you only need to win three of those ten games to ensure winning the division. Each time you win, your Magic Number goes down by one.