I have the simplest sort of coffee grinder. It looks roughly like this. The unit in the picture claims a $50 list price, but I bought mine in 1985 for $10. There are a lot of knocks on this kind of grinder. It can burn the grounds, and these cheap grinders don't last very long. Except for mine.
When I bought it, I could see that the grinder's weak point was its easily overheated motor. Metal fatigue usually ruins little hot-running devices. So I decided never to run it more than ten seconds at a time. These days I run it for 9 seconds, give it 9 minutes rest, then another 9 seconds, and maybe one more such cycle, to grind my coffee beans. The unit still works.
Actually it broke today, but for a fascinating reason: the a/c power cord wore out. Both the insulation and the wire broke. To me, this particular problem validates the way I've use the grinder. Its designers never expected it to last so long that it would need a higher quality power cord.
I fixed it for another $5. I doubt it will last another twenty years; but I doubt I'll be grinding coffee in twenty years, anyway.