Breaker failure is not that rare. I've seen a bunch of them, and have two in my shop at the moment which failed.
Failure can be of several types, including:
1. inability, over time, to carry the rated load (i.e., early tripping);
2. corroded contacts;
3. burned and frozen contacts;
4. physical failure of the housing or internal parts
(cracking of the typical plastic housing will do it); and
5. bad design (Blue Sea Systems did a makeover/recall/model switch as few years back for this reason).
So, the poster who said, "BULL" is dead on...except for the fact that it's quite common, not rare at all.
I've seen enough failures, including on my on boat, that a couple of years ago I replaced my anchor windlass
breaker with a small battery
switch and a hefty ANL fuse. No problems since.