Where does the term "wrench attack" come from, used to describe physical attacks against cryptocurrency holders?

This name comes from a webcomic strip *xkcd* (strip #538), published by Randall Munroe, which illustrated the absurdity of breaking an unbreakable mathematical encryption...
Why attack the algorithm when you can simply hit the person with a wrench until they give up their password?
Indeed, if someone knows you hold Bitcoin, the most robust cryptography in the world won't protect you from a man with a tool and enough determination...