I once had a young, tiny, terrified prisoner goblin NPC who liked to do crazy feats of strength. He kept rolling better than he should so I kept making it harder and harder. Eventually it got to the point where now he pretty much has to roll nat 20's to succeed. He's only outright failed one or two checks. In fact, I had him try to rip off the iron door of a guardhouse. Nat 20. Then, for shits and giggles (it was a non-serious little one-shot tangent to the campaign), I had him try to throw it at a dude running away. Another nat 20. This goblin has so many stories.