These young guys are like all young men: they have to learn that what they thought was how things were in college is child's play compared to "adult life" as a professional paid in whatever field. And, just like young folks going into the military, they have to learn that they can perform even when they think there's not enough left in them to do it. They have to learn to push through.
As McVay says, it's all part of maturation process. And I imagine McVay really knows how to give it to those young guys when they don't live up to expectations. Sadly, there will be those that will NOT learn to push through, and soon they'll be on another team or on the street.
