They played scared and not to lose yesterday. I do agree with you that many BYU teams look afraid to fail rather than confident in their ability to win. I'm sure the players know BYU's history and reputation of being underachievers in the tournament. They were not mentally prepared. Part of that is on Pope and part of that is on the players themselves. They were also unprepared for the physicality that Duquesne played with and Pope even admitted it.
I disagree, though, with your idea that players who keep their emotions in-check can't achieve excellence because they don't allow themselves to be vulnerable. I was a player that preferred to keep my emotions in-check so I could focus on what I needed to do rather than ride the emotional roller coaster and be up and down. In the most pressure packed game I ever played in, I played very well and I would say it was largely because I didn't ride my emotions.
IMHO Pope made some errors with the lineup and it appeared that he treated it as just another regular season game. The starting five was awful to start the game. That should've been the last we saw of that group all together on the floor that game, instead Pope ran them out together to start the 2nd half and that went about as well as it did to start the game. In an elimination game, you don't have the luxury of "sticking to the rotation".