This is a post by Oscar Piedrahita (University of Barcelona).

You’re mowing your lawn when your neighbor strolls over and asks, “Do you know how many blades of grass you’ve just cut?” You’d naturally answer no. But if they then say “So you’re ignorant of that fact?”, this second question would feel  stilted, perhaps even misplaced. Is this something you’re supposed to know? Of course you don’t know the count, but calling you ignorant of that trivial detail sounds like an unwarranted criticism.