[thenobsta]

Seems like he's describing homeostasis and hormesis.

The body has a homeostatic balance physically and psychologically. Pushing yourself out that balance (the comfort zone) induces and adaptation (growth). When you push yourself into the edge, as he defines it, you enter the hormetic zone, the area of the dose response where there is benefit (be it from physical or psychological stressors or medicines). Going too far causes unbeneficial and possibly irreparable damage.