Worth it?

Yesterday I talked about a painting that took almost a year to complete. This relates to a question I have been asking myself lately - is painting "worth it"?
You put many hours of your life into a painting. What is necessary, if anything, for it to have been "worth it"? Does that painting need to sell for a certain amount of money? Do you need a certain amount of reaction from people? Does the painting need to get into galleries and shows?
I must admit that I sometimes feel like certain paintings were "a waste". This is often based on the reaction to the painting; if it wasn't well-received, I feel like, "Was it even worth it to paint that?"

When I first started painting, I didn't really care about how the painting "did" after I painted it - I just focused on enjoying the painting. I plan to start getting back to how I was back then.