It's a bit like finals in college. I knew that without the stress from the threat of failing the finals, I wouldn't apply myself to learning the material. Stress brings out the best in people.

It's like "angle of attack" in a wing (funnily enough, given the topic).

Increasing it works up to a point (increasing lift) but at the cost of increased drag and, at a certain point, a stall. I've found myself, at different points, "coasting" (gliding) and "stalling" (pulling up too hard when I'm not in the right conditions). Long-term burnout is like being "behind the power curve" and gradually losing energy.