Consciously.
Maliciously.
My printer, for example, happily prints away for years.
Today, for the first time in yonks, I actually really NEED some documents printing for Very Important Work and the damn thing has died on me.
It waited.
I promise you, it waited.
It's printed out oodles of supermario pics for the kids, it's printed maps no problem since we got the satnav
, but today it sensed something Important and it's taken itself off to printer heaven just to spite me.
Probably laughing as it went.
Bastard.