Schrodinger's ninja

A person who is not wearing a mask, but still somehow manages to sneak into a place where masks are required, especially when there are guards at the entrance.

I was so confused! This man must have been a ninja to have been able to so easily sneak in without a mask. But if he actually was a ninja, then he would have been wearing a mask anyways! What manner of strange creature was this who was both a ninja and not? It was Schrodinger's ninja!