WHEN IS IT *GOOD* TO ABANDON A PROJECT?

I had this feeling with my first game, which I just released. Most time, I didn't enjoy making the game because it took too long to make. When I started it, I had little to nothing planned. All I thought was: I need to finish a game for once and this game will be pretty easy to make. It wasn't easy, but I kept going just for the dream of releasing my very own game.
One should be careful when struggling with things like these. It can destroy you if you're unlucky.
Morale of the story: Start simple and build from that and have a basic plan so you'll know what you're up against!

I never do it. In general, i put the project back and take it in some time.