When willpower is on the verge, they shift the mindset of a tired tri-athlete:  just keep going, you can do it.

DeWall C. N., Baumeister, R. F., Mead, N. L., & Vohs, K. D. (2011). How leaders self-regulate their task performance: Evidence that power promotes diligence, depletion, and disdain. Journal of Personality and Social Psychology, 100, 47-65.