Interesting means productive →

When you have a natural interest in something, your productivity goes through the roof. Even though whatever I’m naturally interested in might not, from an objective point of view, be the most important thing to work on at that time, it is the most important thing to work on because of the productivity gains I get out of just being super fired-up about it. I have to get that out of my system. And I wind up doing things really quickly.

When you’re not working on something you’re inspired by, your efficiency is so much lower. You find more moments in the day to let yourself be distracted by email or reading on the Web or something else. That’s usually the key smell I detect when I’m working on something I don’t really want to be working on: I check email much more frequently and I engage in chats about things that aren’t related to what I should be working on.

Whatever interests you naturally is the most important thing to work on — 37 Signals

Sounds like me.