Player – I fire my rpg.

DM – OK, roll to see if you hit the target.

Player – Darn, a 1

DM – OK, so, you have a misfire, but the projectile does clear the launcher. Roll again to see what it does.

Player – Wow, a 20.

DM – Hmm. OK, so you don’t hit the target in a normal fashion, but the warhead shoots out, hits the ground about 25 meters in front of you, then bounces three times before landing on the target and exploding.

Player – …..

Player – You mean….

DM – Yes, you catastrophically failed successfully.