The Key

Standing at my door in the dark, I tried every key on my keychain, but none would work even though one was surely my housekey! I even tried them both ways. Frustrated, I went out to the streetlight to locate the right one. When I went back and tried it in the dark, the door clicked open right away.

Presumably, the only difference was the knowledge that I had the right key.

It reminds me of cases where professors have put unsolved research problems on exams. Every now and then, a bright student will solve one. In this case, they are unburdened by the "knowledge" that the problem is hard or possibly insoluble.