In sport if an athlete is made to train they will in time quit – they need to want it. An effort of will or effort is tiring. If you have had to force yourself to do something or made to do it your resistance to the temptations to do something else will weaken. This is known as ego depletion. After Roy Baumeister (1998) in Daniel Kahneman’s 2011book ‘Thinking, fast and slow’.