Murphy's Law has numerous extensions and corollaries. The most important in my experience is:

"If it can't hurt you by going wrong, then it won't!"

Thus if you've backed up your files recently, your disk won't crash. If you've printed out a good-enough-to-turn-in draft of a term paper then your printer won't run out of ink when you ask it to produce the final version. If you arrange your travel schedule to arrive early for an appointment then the bus won't be late, there will be plenty of taxis, your flight won't be cancelled, traffic will be exceptionally light, and so forth. If you hang on to your receipts, you won't need them. And if you buy insurance, you'll never collect.

TopicHumor - TopicLife - 2003-12-17

(correlates: BetterFasterCheaper, MisterChristmas, DishonorAmongThieves, ...)