I was handed a problem during a job interview that was a "how do you get a computer to do this?" problem. Apparently I was the only one who attempted, and the general consensus is that no, you need a human being to do it.

So I sometimes divide problems into "Can a human do it or not?"

(Years later I would finally have the inklings of how to get a computer to do it. It would be quite complex but I think it might actually be feasible. A lot of subconscious introspection happened.)