That's why he's having such a difficult time understanding why the same knee gave out on Saturday, costing him the season and a chance to end his career with fellow seniors E'Twaun Moore and JaJuan Johnson.
Hummel spoke to the media Wednesday for the first time since the school announced the injury. He said he landed awkwardly on the knee when he went up for a block during a drill.
"I felt it pop again," he said, "and I knew right away it was my ACL."
Hummel was second on the team with 15.7 points and 6.9 rebounds per game before he tore the ACL this past February against Minnesota. The Boilermakers were ranked No. 3 when he was hurt, then stumbled without him before recovering to reach the round of 16 in the NCAA tournament.
He had surgery in March and appeared ready for the season.
"I felt good," Hummel said. "I was starting to be able to dunk the ball pretty easily. I shot the basketball pretty well all summer and fall. That's what's probably part of the reason why it's so frustrating, because I felt pretty good. I was moving around pretty good, and to have this happen again is hard to swallow."
Now, he's focused now on rehabilitiation so he can redshirt this season and return next year. He plans to have surgery in early November.
"It never even crossed my mind to stop playing," Hummel said. "I'm definitely not going to give up that easy."
Purdue coach Matt Painter said Hummel is mature, but human.
"He's been through some tough times with his injuries," Painter said. "Even though he does a good job of handling things, it's frustrating. But he doesn't come off that way. He moves forward and takes on the next challenge, and that's preparing for surgery."
Hummel appeared to be ready to at least test the knee.
"Rob started doing good things, started making improvements," Painter said. "I watched him and it's like, 'Hey, he's getting back, he's getting back to making that stride,' but he wasn't the same guy. Nobody is."
Hummel missed only one game as a high school player, so perhaps that's why he's at a loss to understand why he's had three major injuries since he arrived at Purdue. Hummel missed several games two seasons ago with a back injury as well.
"Three years of playing varsity ball, I missed one game for a concussion," he said. "I really was never hurt in high school, middle school, AAU and elementary school. I don't know what's going on. I was really never hurt."
Painter said he was impressed with Hummel's diligence after the tear in February.
"He worked so hard," Painter said. "You take care of your everyday business with your rehab and you do what you're supposed to do, and then it happens again."
His teammates have been supportive.
"In terms of words, there's not much you can say," Hummel said. "I know I'm frustrated. Everybody is."
Hummel is focused on getting the swelling out of his knee and regaining his range of motion. Eventually, he expects to look like himself on the court.
"I still think I can come back and play at a high level," he said. "I'm not concerned about not being able to come back. I know there's people who have torn their ACLs two and three times and come back."