There are very few things in the mind which eat up as much energy as worry. It is one of the most difficult things not to worry about anything. Worry is experienced when things go wrong, but in relation to past happenings it is idle merely to wish that they might have been otherwise. The frozen past is what it is, and no amount of worrying is going to make it other than what it has been. But the limited ego-mind identifies itself with its past, gets entangled with it and keeps alive the pangs of frustrated desires.