What makes an artist great?

It is his/her ability to stay as a well of ideas because passion keeps him/her alive. Paint and canvas can be bought, but inspiration can't.

Once an artist goes commercial, the well gets untended then later on abandoned.

Which is why some "artists" remain, at the end of the day, remains uninspired--even if they already have reached some height that for them meant "greatness."

To the real artist, it's not greatness, it's just a 5 cent pass to get yourself dressed up in a robe and have yourself photographed on a pedestal. After that, you're done, and the man next in line moves on as the gatekeeper of the studio says "NEXT!"