A discussion on burnout here[0] last year called burnout "a kind of unrequited love." I don't know that it's a perfect metaphor, but it's changed the way I approach my attitude and commitment to work. This article touches on that idea under "Prevent Ineffectiveness." The times I've felt most burnt out aren't always when I'm working the hardest, but when I'm working the hardest without getting enough in return. When working on a project I am passionate about or I control, I can work much harder without burnout creeping in.
[0]: https://news.ycombinator.com/item?id=28307721