When I was in high school I was naturally thin. I ate crap, tons of it, and all the time. And I never exercised. I was like 135 pounds. I totally took that for granted, so I never had a healthy lifestyle until now.
I think that when I reach my goal (I don't even know what it is, but 140-145 and 25% body fat sounds nice) I will totally be able to keep this up indefinitely. It feels good to live healthily.