Calvin Johnson had a goal to be the best receiver ever just because he knew he could be. And now, at the age of 30, Megatron is likely about to walk away from the game.

Q: “Do you have a goal to be the best receiver ever?”

CALVIN JOHNSON: “Yeah. No doubt.”

That was three years and seven weeks ago. Now here is Calvin Johnson, 30 years old and coming off an 88-catch, 1,214-yard year ... strongly considering retirement. He has reportedly informed his coach Jim Caldwell that 2015 was his last season.

It’s a shocking story, unless you know Johnson. Then it’s not even surprising. Men play pro football for many reasons: to build a better life for their family, to become famous, to win a ring, to make football history, or to buy a Bentley that they can drive when their Lamborghini is in the shop. Some are adrenaline junkies, others are addicted to winning, and many are drawn to the sport’s legal violence.

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Calvin Johnson played football because he was really good at it. He was 6’5” and 237 pounds and ran the 40-yard dash in 4.35 seconds. Nobody could cover him. He wanted to be the best receiver ever, but not because of the adulation it would bring, and not to prove a point to anybody. Just because he knew that he could be.

And after a productive rookie year—756 yards for a mediocre Detriot Lions team—Johnson realized he was coasting. This was not how he was raised. Johnson’s father, Calvin Sr., was a freight-train conductor for Norfolk Southern Railways. Calvin Sr. kept working for years after his son became a multimillionaire, and it wasn’t for the money or to get in some freight-conductor Hall of Fame.

Calvin Johnson Sr. believed in an honest day’s work. His son started putting in a whole bunch of them. He mastered his routes, refined his skills, and made some of the most difficult catches in league history.

Johnson looked at LeBron James and thought: I’m like him. He never cared about the global-icon bit—Johnson is a reluctant interviewee, incapable of self-promotion, and though he did some commercials, his heart was never in the endorsement game. (He said he donated all his endorsement income to his foundation for at-risk youth.) But he remembered watching James as a young player.

“People on TV were watching LeBron, like, ‘Does he know if he drives to the hole every time, he is going to get fouled or he is going to make the bucket?'” Johnson said. “It was kind of like that with me.”

He decided he should have at least 100 receiving yards in every game, because “it’s easy for me to do that. That’s the minimum.” He was not bragging. He was chastising himself for the times he fell short. His former teammate, Roy Williams, dubbed him Megatron, but Johnson never fell for the myth that football made him some kind of superhero. This was his job.

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If he retires, it would be easy to pin this on the Lions’ ineptitude. But ESPN reported that Johnson told people last summer that the 2015 season would be his last, and the Lions were coming off an 11–5 season. Johnson is not the type to walk away because he thinks he deserved to win more. He has always made his biggest demands of himself.

Before the 2012 season, Johnson told SI that a 2,000-yard receiving season was “definitely possible.” Jerry Rice’s NFL record was 1,848. Johnson finished that season with 1,964, the season-long equivalent of Babe Ruth’s called shot. He was proud but not overly impressed. He thought he could have had more.

That record-breaking 2012 season was the peak of Megatron and the beginning of his demise. He played through an injured foot, an injured ankle and two injured knees that season, and on the day he acknowledged that he hoped to be the best ever, he held out his hands and surveyed the damage:

“This one won’t straighten out ...this one hurts to catch...this one’s messed up. This one’s coming back—this one was real swollen, this is getting better, though…”

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Johnson is tough, but he is also smart, and he knew the game that made him rich was exacting its price. He could keep going. He could try to set more records and win a Super Bowl and solidify his place in the Hall of Fame, but those are just things we tell him he should want.

He has been Megatron for a few years, but he has been Calvin Johnson, Jr. for his whole life. He did Calvin Johnson, Sr. proud. I suspect that’s enough for him, no matter what we think.