This seems to be related to the concept of flow: finding that sweet spot between being too relaxed and too-stressed out. We need a moderate dose of stress to perform at our best. What's so interesting is that experiencing flow is also correlated with long-term fullfillment.

I've recently theorized the single most important factor for happiness and performance is being able to control your stress levels and increase/decrease your stress levels at will. It is not novel, but it helps me if I see my primary task as identifying which mechanisms can help me lower or increase stress. So far, meditation seems to have the best effect.