He knows all about art, but he doesn't know what he likes.
Notes from Wikiquote
"Word Dance — Part One", A Thurber Carnival (1960)
Variants
He knew all about art, but he didn't know what you like.
It is better to ask some of the questions than to know all the answers.
There are two kinds of light — the glow that illumines, and the glare that obscures.
Quote text and notes from Wikiquote: James Thurber (page history), available under CC BY-SA 4.0. Source quality and labels are our own summary of what Wikiquote records.