"The bear cannot find a frog."
Translation:곰이 개구리를 못 찾아요.
No. As a native Korean speaker, I've never heard that as a proverb... Perhaps it is just one of the assembled sentence from fragments.
I'm not korean but I heard of a saying about a frog and a well if that's what you're talking about. The frog is narrowsighted and thinks the well is the whole world. Something like that
The former implies inability, i.e. can't do something.
The latter is a simple negation, i.e. doesn't do something.
이것을 안 먹어요. I don't eat this.
이걸 못 먹어요. I can't eat this.