Or debuggers that would take out the entire OS.
Or a bad driver crashing everything multiple times a week.
Or a misbehaving process not handing control back to the OS.
I grew up in the era of 8 and 16 bit micros and early PCs, they where hilariously less stable than modern machines while doing far less, there wasn’t some halcyon age of near perfect software, it’s always been a case of things been good enough to be good enough but at least operating systems did improve.