Death is a teacher. It bestows hard lessons upon those who remain. Among that which I learned when my mom passed unexpectedly several years ago is that no one truly knows what anyone else is going through in these times.

Every situation is its own waking nightmare. We can understand some of it, but not all. Grief is not an off-the-rack entity; it is custom fit for each set of circumstances.

Thus, Kevin McHale couldn’t know all the intricacies of Isaiah Thomas’ anguish following the death of his sister last Saturday, but he had a better grasp of the concept than most, though no one would wish him his expertise.

On Nov. 24, 2012, Kevin and Lynn McHale’s daughter Alexandra (Sasha to all) succumbed to complications from lupus. Then coach of the Rockets, Kevin took nearly a month away from his job in the weeks surrounding that date. His eyes were red and glassy at the morning shootaround when he returned to coach against the Celtics on Dec. 14.

Now a commentator for TNT, McHale felt familiar vibrations when he entered the Celtics confines before the start of this first-round playoff series against Chicago. He maybe couldn’t have guessed his old club would lose the first two games, but he sensed difficulty as the Celts tried to come to grips with their hurt for Thomas, his unspeakable pain and the impending Game 1.

“Well, I knew the poor guy was completely numb,” said McHale, “and all the well wishes and everything else, while they’re very nice, they don’t make any difference when it comes to a game. This is more than that, and nothing’s going to change the situation. Time doesn’t even change the situation.

“I could just tell he was just absolutely numb. I was just surprised he was playing. I admired the fact that he played. I just looked at him and thought, he’s just going to go out there and compete because that’s what he does. I was hoping he’d be able to lose himself in the game and just enjoy himself just for a little bit.”

It was a hope expressed by many, but while Thomas went for 33 points, his sweat was mixed with tears. He was inconsolable prior to the 106-102 loss, and he was more visibly off his game as the 90.9 percent free throw shooter missed 6-of-13 from the line on the way to 20 points in a 111-97 defeat Tuesday.

“With basketball, there’s a pleasure and there’s a release in playing,” McHale said. “But I just felt for him. You’re numb and the world’s completely spinning. It’s spinning really, really fast and it’s not slowing down.

“The poor kid’s got it tough. The whole family’s got it tough. They’ve got a tough two or three years ahead of them.”

McHale may not know all the details of the Thomas family ties, but he is a man of empathy, and he knows the look of sudden loss.

“I saw Isaiah and I just went, like, whoa. I could see it,” McHale said. “It’s one of those things that you never, ever want anybody to go through. It’s a devastating pain, and it’s never-ending. It never really goes away, and there’s nothing you can ever say.

“There’s nothing I could say to him. There’s nothing you can say to anybody, because at the end of the day, the thing you want the most is for the person to come back, and they never will. So it’s impossible to deal with. I just . . . I just felt terrible for him.”

It is expected that Thomas, after a flight to Tacoma, Wash., to be with family, will return to the Celtics for tomorrow night’s Game 3 in Chicago. He will try, once again, to let the competition push aside his heartache, if only for a while.

“That’s the only chance he has at some relief, to go out there and just play the game and lose yourself in the game as best you can,” McHale said. “But at that point, you’re dealing pretty much on just instinct. Nothing’s sharp. Your mind’s not sharp. Your body’s not sharp. You don’t sleep. It just is a …”

His voice trailed off as he thought back to watching Thomas perform in public during the most private of times.

“I just looked at him and I just admired the fact he went out there,” McHale said. “I was happy for him that he was at least able to do that and get a little bit of relief. Even for 10 or 15 minutes, to get a little bit of, ‘I’m part of my team. I’m out here.’ Stuff like that.

“But it’s hard, because in your brain, you know the minute that horn sounds, you’re right back into a terrible, terrible spot.”

A spot no one else can fully comprehend.