"Persistence is not just about pushing forward; it is about pushing through to reach a new height, exceeding a limit you thought you had. Everbody limits themselves in some way, whether it is to manage expectations and avoid disappointment, or to avoid the physical pain and discomfort that accompanies the reach for a new limit, a higher standard. It takes toughness to push your limits, to push through being tired, to push past muscle fatigue to muscle failure.  Are you, individually and as a team, tough enough to push past what you think is a breaking point and reach a new height? Pushing your limits is a critical element of toughness. " 

from "Toughness" by Jay Bilas