Richard Feynman Quote

Anyway, I have to argue about flying saucers on the beach with people, you know. And I was interested in this: they keep arguing that it is possible. And that's true. It is possible. They do not appreciate that the problem is not to demonstrate whether it's possible or not but whether it's going on or not.

lecture III: "This Unscientific Age" - The Meaning of It All (1999)