I saw Kruger speak about playing for Hartman. He said Hartman was very hard on guys and he chose to be a more positive motivator. (He did not insult Hartman, in fact he complimented and said he was a great coach.)
You can see why players call what Lon has created at OU a family atmosphere. When players genuinely care about each other, they're all about doing what they can to help the team win games.