I'm sure it's not my theory really. Plenty of folks have probably given it much more insightful and philosophical names and definitions.
But the way I see it, if things are going really well for an individual — like, surprisingly well — then said individual will probably, in the near future, experience "shit hitting the fan," as I'm fond of saying. I'm also fond of commas tonight, apparently. And I'm much too tired to edit anything else.
All I'm trying to say is if the universe throws too many good things your way, you should be nervous. Because something hiding around the bend is bound to come along and make sure you bottom out low enough to balance out your highest high.
That is my very scientific and slightly pessimistic theory. Enjoy.