On Christmas Day, it will be 20 years since Michael Jackson’s “Thriller” album debuted on the pop charts. Twenty years since the rules changed, 20 years since the record book was rewritten, 20 years since the onset of a globe-straddling phenomenon.

And 20 years since Michael Jackson disappeared.

I know what you’re saying. “What do you mean, disappeared? Didn’t I just see him on television, dangling his baby over a balcony? Didn’t I hear about him going to court wearing a surgical mask? Wasn’t that him I saw on the supermarket tabloid, a skeleton man with owl eyes, lipless mouth, ruined nose and skin the color and texture of parchment?”

But that’s not Michael Jackson. Or at least it wasn’t, 20 years ago. Back then, Michael Jackson was a handsome man with brown skin, a normal nose and lips. Then he exploded. Became one of the biggest stars in the history of stars.

I don’t think it’s coincidental that he simultaneously began fading into what he is now. Which is, for all intents and purposes, someone from space. Someone we find strange and not a little repulsive, someone we laugh at, but uncomfortably, defensively, reflexively, as if he troubles us in ways we do not otherwise know how to express.

It is, all in all, a cautionary tale for a nation besotted with the idea that lives lived in spotlight glare are somehow inherently superior to those lived in shadow. A warning story for the generation of “American Idol” and “The Bachelor,” nonstop media and “superstars” no one ever heard of two weeks ago. It is a reminder:

Fame is not its own reward. Fame does not make you smarter, your jokes funnier, your breath sweeter. Sometimes, all fame does is make people bow, curtsy, kiss your fanny and fear to tell you any word that isn’t yes.

Even those who should know better. Like Michael’s older brother, Jermaine, who shows up regularly on entertainment news programs to defend his sibling from slurs and accusations arising from the strangeness of his behavior.

Certainly, one can’t blame a guy for standing up for his brother. But every time I see Jermaine blaming Michael’s problems on media excess or public misunderstanding, I wonder if even he believes it, if he or any member of their family, or any friend, or any EMPLOYEE, even, has ever once had the guts to say, Michael, that’s enough plastic surgery. Michael, you shouldn’t have sleepovers with children. Michael, no.

And would it have made a difference if they did?

Sometimes, fame means nobody places any limits on your behavior. And that’s a dangerous thing, because we all need to be held in check sometimes, all need to be told when we have misbehaved, wandered astray. This is one of the ways we learn to live in the world.

If Michael ever knew, he forgot a long time ago.

It’s an affliction peculiar to celebrities. Think Mike Tyson, a walking temper tantrum with lethal fists. Think Winona Ryder, stealing what she can afford many times over. Think Whitney Houston, acknowledging frequent drug use, but taking offense at the notion that she might ever do crack. “I make too much for me to ever smoke crack,” she told Diane Sawyer. As if we should be impressed that she’s an upscale junkie.

But of all of them, it’s Michael who makes me most sad.

Part of that is because he seems the most extreme example of how fame can untether perception and unravel reality. He is the most visceral reminder that the ability to indulge every whim is no blessing.

But the other component of that sadness is simply, selfishly, that he’s someone I used to like. He’s someone whose supple tenor once had me camping out at the record store, someone whose frictionless feet made me stay up late to catch him on Johnny Carson.

Twenty years ago, Michael Jackson was a talented guy who entertained me. But that man has long since disappeared and I don’t know where he’s gone.

What’s worse is, I don’t think he knows, himself.

— Leonard Pitts Jr. is a columnist for the Miami Herald.