It all depends on your personal standards. This is a much more measured take than what I wrote above, and probably more accurate. Of course, Sturgeon's Law is obviously not literally true in every domain. 90% of people can successfully fry an egg, etc.

60% feels about right - they can get stuff done but I have to intervene because the damage they are causing is just beyond their ability to recognize (and I'm sure I do this too, for harder problems).