attiny - How often do AVR's actually glitch and need a watch-dog reset in the real-world?

Have you ever seen an otherwise happy AVR spontaneously glitch and require a reset?

Assuming:

1. a nice stead power supply that stays inside the specified range


2. a correctly sized decoupling cap directly between Vcc and ground


3. normal (not too noisy) household conditions

...what is the real-world MTB glitches?

I've had hundreds of AVR's running for years and I don't think I ever have seen a real glitch, but maybe I am just lucky?

Note that I know that you should always use a watchdog, I know. Don't flame me - but if the likelihood of glitches is very low, there could be applications where it would be reasonable to maybe not use the watchdog to get lower power usage in sleep.

Note also that I understand that the watchdog also protects you from firmware bugs, but I am only asking about spontaneous hardware glitches.