Match-to-match, the question that materializes time and again out of that fog of unforced errors and poor footwork is: "Will Serena come out of it, find her game, win again?"

It often appears that she's running on fumes, and perhaps in some ways that's true. But she is a woman of remarkable physical and emotional strength and will, and if that isn't enough, there's always that ability to exercise the equivalent of the nuclear option: that magnificent serve.

-- ESPN

This quote brings to mind what the Flow book says about emotions and will (... At least as much as intelligence, it [control over consciousness] requires the commitment of emotions and will ...)