All you have to do is look at a million paintings

Circe Berman has just asked me how to tell a good painting from a bad one.

I said that the best answer I had ever heard to that question, although imperfect, came from a painter named Syd Solomon [...]

"How can you tell a good painting from a bad one? [...] All you have to do my dear," he said, "is look at a million paintings, and then you can never be mistaken."

It's true! It's true!

Kurt Vonnegut, Bluebeard (1987), p165. This being Vonnegut, it's possible that Solomon didn't actually say that. Nonetheless, it's very good.