What does the idiom 'cut the mustard' mean?

Answer 1

Cut the mustard: to be able to handle a difficult job or fulfill the requirements

If something doesn't cut the mustard, it means that it does not meet necessary requirements or expectations. For example,

"My wife is mad at me for missing our anniversary. I bought her a bouquet of flowers, but that just didn't cut the mustard."

The idiom "can't cut the mustard" means not being able to handle difficult situations.
It means whatever it is is not sufficient, that more is required.
"Can't cut the mustard" means something doesn't meet standard expectations.

Answer 2

I believe the more common acceptance of "Cut the mustard" comes from "cutting" or diluting mustard with vinegar. By cutting mustard with vinegar, it makes it taste better. So, someone that was very good at "cutting the mustard" was regarded as skilled. But if someone was not as skilled at the proper dilution of vinegar to mustard, it was said, "he couldn't cut the mustard". The term cut is similarly used today when referring to "cutting" a drug, such as heroin. Some people believe that mustard might have been confused with muster. But, not one single case of past use shows that variation. So, I don't believe this is a likely answer.