We were witnesses, all right — witness to a flat-out schooling by men who once took their own lumps on the NBA’s grandest stage, who didn’t turn their free agent signings into a WWE Raw event before they had won bupkus, who knew the pain of losing here hurt too much to treat getting out of the second round like Carnival in Rio.

And now that Dirk and Dallas’s locker room of redemption has sent the Heat and The Forsaken One into a shell-shocked summer of frustration — one only Dan Gilbert and northeastern Ohio could understand last July when LeBron left without a note (karma’s a killer, young fella) — now comes the lesson to take with him:

Of all the things LeBron James could learn from the past 11 months, and especially the past two weeks, none is more important than the message Jason Kidd and DeShawn Stevenson communicated on Sunday night, the night an old point guard, one 7-foot all-star, a hell of a bench and their teammates dropped the game’s most talented trio to capture the NBA championship:

Being famous and young guarantees nothing.

Ask Kidd, who won his first championship in his 17th year. He knows being lauded as one of the greatest of all-time as a teenager is not a prerequisite to win a title.

“Long wait,” he said, his eyes either red from tears or champagne on Sunday night. “What a journey, man, what a journey.”

Ask Stevenson, another preps-to-pros phenom who lost his explosiveness to injury, feuded with Jerry Sloan in Utah and eventually learned to play defense and knock down important three-pointers, like those in the first half of Game 6. He disrupted people like Udonis Haslem and Mario Chalmers, who all got technical fouls after a fracas in the first half.

“Worst to first! Worst to first!” Stevenson, Haywood and an injured Caron Butler chanted as they hugged one another after Dallas had closed Miami out, 105-95, referring to leaving the 19- and 26-win Wizards more than a year ago to join an NBA champion in 2011.

“My thing was, even after I couldn’t jump like I used to and people thought I was done, I just did what I could to hang around and stay in the league,” Stevenson added.

Kidd, once the phenom LeBron was, though not as hyped, is 38 years and 81 days old. In his third Finals try, he dusted off his three-point shot, let the ball do the work, used his large, strong mitts to compensate for his inability to stay with LeBron or Dwyane Wade laterally and, best of all, let Dirk be Dirk for a championship coveted for more than 20 years.

“What a warrior he is at 38, chasing one of the most athletic players in this league out there and doing a great job on him,” Nowitzki said after he was named Finals MVP, parlaying a 1-for-12 first half into a 21-point game.

This wasn’t just an NBA Finals for the ages — it was for the aged, the second-chance lifers in the game just wanting one more shot to win it all.

For Nowitzki, who at 32 years old and 13 years in the league was incomparable, erasing any memory of the Mavericks’ meltdown in Miami five years ago in the Finals.

For Kidd, 0-2 with New Jersey nearly 10 years ago.

For Terry, whose Game 6 output (27 points) keyed this victory until Dirk could take over down the stretch.

And, yes, for Rick Carlisle, 0-2 with Detroit in the Finals, and Mark Cuban, the young, impetuous owner of many years ago who actually was loyal to Nowitzki when everyone thought he was no longer an elite player who could lead his team to a title.

Kidd’s story, though, is one that will be lost today because of the LeBron furor and the collapse of a team favored to win it all in their first year together. And it shouldn’t be.

Asked after Game 5 whether winning the title would be for every kid from Oakland’s Mosswood Park. Or for every Bay Area star like playground king Demetrius “Hook” Mitchell who did jail time and never had the good fortune to play in the NBA like Kidd or Gary Payton or, before them, Bill Russell or Paul Silas. Kidd paused to think about it.

“Not really,” he said. “I’m happy to represent where I’m from and who didn’t make it. But really I just identify with old people. Old players. The guys who just are sore, had a bunch of surgeries, can’t believe they’re still out there trying to take on the young guys at the Y or whatever. Yep, just old dudes.”

Confession: I had a built-in bias in the Finals. No, it wasn’t because Nowitzki is from my mother’s home town of Wurzburg, Germany, (Pop. 133,000) — the Bavarian postcard my parents met and were married in while my father was a serviceman.

I was rooting for Kidd to finally get a ring. As a high school correspondent, I was at his coming-out party — so to speak. Outside of national hoop circles, no one had heard of the 16-year-old who, as a sophomore at St. Joseph’s High School in Alameda, started against mighty Skyline in the state, large-school semifinals in 1991.

Well, no one but the Oakland Coliseum security guard who ran exasperated into the pressroom as the roars from the stands grew louder.

“Oh my God! This kid from St. Joe’s is takin’ out Skyline by himself,” he said, his pupils enlarged. “I’ve seen the truth. It’s him.”

We saw back-to-back steals at halfcourt, whereby Kidd raced toward the goal at warp speed and dunked on two 6-foot-8 seniors, right between them. We saw a double-digit Skyline lead evaporate within two minutes in the fourth quarter, Kidd hitting teammates in stride with bullet, no-look passes.

It was a smaller, stockier Magic — at 16!

Twenty-two years later, there was that kid, at 38, doing all the little things to fend off a younger, talented team.

With 6 minutes 11 seconds left in the third quarter, he dropped in a three-pointer to push Dallas ahead by six points. Two minutes later, he drew a charge from Dwyane Wade under the basket. Years ago he might have gone for the steal, but he knows it’s Wade and LeBron’s league now and the only way to beat them is with your head and heart.

With 47.7 seconds left and the shot clock winding down, he dropped in a three-pointer in the third. He snuffed out Miami’s last genuine rally, too, when Mario Chalmers seemed to have him beat for a layup. He went up, stripped the ball and Dallas took over.

Afterward it was all about LeBron, because in this era of scrutiny we pay too much attention to what players didn’t do rather than celebrating who did it to them. He was asked if it was a personal failure, losing to a team the Heat were favored to beat.

“Every time you get to the top of the mountain and you fall off, it’s a personal failure,” LeBron said, vowing he would back.

But if he really needs to take anything away from this loss, it should be seeing the image of Kidd, hoarse-voiced, celebrating on Miami’s court for all the marbles, years after they called him a phenom, a can’t-miss player.

The losses over the years, he will find out, make the last victory of the season that much sweeter.

Now that school’s out for the summer, one more thing he could learn from Kidd and the Mavericks: Don’t treat a playoff victory like it’s for the championship — until it is.