Isn’t that part of the whole role of the fitness staff as well?
I think great fitness staff build belief and confidence really well. They create a mindset in the players that they have done the work and they are capable of outlasting anyone. Darren Burgess is particularly good in that space, he has the guys believing they are fitter than anyone else which gives them a confidence when they play.
It's like any coach though, you can be the greatest of all time but ultimately the players have to get it done. When it comes to the 20 minute mark of the last quarter it is about the will and want of the player and all the coach can do is hope they execute.