Must Art be Seen?

I asked this question last year on Twitter and I got an excellent response, but I can’t remember what everyone said.

This time, I want the discussion on here so I (or you) can come back to it at any time.

The question is simple, but the answer can be complicated.

Does art need to be seen by more than just its creator?

Or more precisely,

If a creator never shares their work, are they creating art?