William McRaven: The purpose of the training is to weed out those both weak-minded and weak physically before you really even begin the hard SEAL training. So there is a lot of demand placed on you physically, but there was also a lot of demand mentally. They put you in situations where you are either not going to succeed or you’re not going to succeed as well as you thought you were going to succeed.  So they will, for example, they used to play a little bit of mind games. They would say, “Okay, we are going to have a four-mile run on the beach.” And as you were closing in on that last couple of hundred meters, they would go, “Oh no, this isn’t the finish line. The finish line is another couple hundred yards down the beach.” And there were a lot of guys who went, “Come on, I was just coming to the finish line.”  “No, the finish line is further on.”  So you learned that maybe there is no finish line, and you learned how to deal with failure, and you learned kind of what is really inside you, because you were tested physically every day.  You were cold, you were wet, you were miserable, and you still had to perform at a certain level.