cut the mustard – fully fitting to - approach is fully - to meet the expectations - meet the requirements
cut the mustard = perform satisfactorily
The expression is often in negative form, as in your example above, but there are positive connotations also.
In the twentieth century, Americans were able to cut the mustard, that is, "to do what is needed." The first evidence comes from O. Henry in 1904: "So I looked around and found a proposition that exactly cut the mustard."
cut the mustard = to do well enough in what needs to be done; to succeed.
He is keen to exchange the first gifts, but the laibon's family first want to see if he can cut the mustard.
These matches were required to show whether the All Blacks tight five were still able to cut the mustard, whether the loose forwards could combine, whether New Zealand could put together a backline attack without having Joe Stanley as the lynch-pin.
His older brothers and sisters helped Max through high school, but he couldn't cut the mustard in college.