Possible causes are too numerous to mention. It's hard to write system software, and that's what extensions are - system software. Extendibility makes the Macintosh interesting, and it comes with a price. Might also be that something needs to be reset but doesn't except during a cold start. Someone or something writing to PRAM unintentionally or incorrectly.
Power failure comes in many forms.
When I explained that it can only hold one, and you have to take it out before you can put another in, she decided that she'd better get that first one out of there. Without hesitation, she reached right up to push the floppy eject button. Having written some Apple system software myself, I can assure you that it's entirely possible that Apple might accidentally ship some system software that has a bug in it. Any errors in the system software may bring it to its knees, no matter what kind of protection is in place. Computers are complicated beasts, and it's extremely tough to cover all the possibilities, memory protection notwithstanding.