This story is part of Peak, The Athletic’s desk covering the mental side of sports. Sign up for Peak’s newsletter here.Kendrick Perkins played 14 years in the NBA. He is now an NBA analyst for ESPN. These are the three best leaders he played with.Kevin Garnett, Boston Celtics forwardEmotionally, his energy was contagious. He showed young guys like myself, Rajon Rondo, “Big Baby” Glen Davis what we needed to do. He showed us how to have a routine, how to get mentally prepared and, most importantly, he showed us how to lock in and limit distractions.And obviously we know about his damn passion. I’ll put it in PG terms. His thinking was: Forget everybody. If you didn’t have Celtics across your chest, you were an enemy.When you walked inside the locker room, it was quiet. There wasn’t talking. He taught us on the day of a game you needed to be locked in. It wasn’t just that you needed to get locked in at the arena on game night. It actually started at shootaround.Throughout the regular season, when we would be walking through plays, he would say to the coaches: “Hold on real quick, y’all. Stop playing around, man. Lock in, man.”We knew right then what it was, so we never had that problem again.It was all about the team.In 2008, we don’t win the championship that year without Kevin Garnett coming to the first day of training camp and saying: “Hey, Doc. Before we start practice, I want to say this: We’re going to run the offense through Paul Pierce and Ray Allen. I’m going to put myself behind those guys, and I’m going to focus on the defensive side.”Right there set the temperature and the tone for the season and for the team.Jalen Brunson and the "underdog effect"Elise DevlinNick Collison, Oklahoma City Thunder forwardBest teammate I ever had.When you talk about losing yourself in the team, he was the true definition of that. The best thing about Nick was that he never switched up.