Here's what else isn't unusual, at least for those of us whose brother is about as close in age as the Harbaugh sons are to each other. There comes a time when the little brat is a match for his older tormentor, when the fight becomes less one-sided than it once was.
There may even come a time, as it did for this tormenting big brother, when the younger one ceases to be the "little" brother, when his force is greater than yours, when the order of the universe as you both know it threatens to get way out of whack.
The younger brother is faced with a choice: Kick his ass and screw with the universe. Or back off.
"I think there's a sense of order to it," my younger brother Tim was saying over the phone Thursday. "Getting beat up by your big brother is kind of expected. Beating up your big brother, you kind of get your mind around how humiliating that is. You're sort of embarrassing your whole family."
This is why I think the Baltimore Ravens are a lock to win Sunday's Super Bowl. Jim Harbaugh turned out to be a better athlete than his big brother John, and as impressive as both coaches' résumés are, Jim's track to this Super Bowl has been warp speed compared to his brother's.
But he is still the little brother when it comes to John, the student with the 3.5 GPA who was diverted from law school and perhaps a career in politics by a love of the game and perhaps a desire to spend more time with a father who, by his own admission this week, was gone from dusk to dawn for much of John's youth.
Including his decadelong stint as an Eagles assistant, John put in his time in learning his craft. He has reached the playoffs in his first five seasons, a feat matched by few coaches.
"I think he's the best in the league at what he does," Jim said this week.
Including you, he was asked?
"I'm half the coach he is," Jim Harbaugh answered. "I don't think there's a coach in the game today that has the full grasp of offense, defense and special teams like my brother does."
Are these pretend platitudes? When little brother lost to big brother on Thanksgiving in 2011, Jim said afterward, "There's a saying that says, 'As iron sharpens iron, so does one man sharpen another.' And I have to say my brother John is the sharpest iron I've ever encountered in my life."
This is not to suggest Jim believes Sunday is predetermined any more than any of us believe it is. Or that any of us do. In fact this is probably the first of the 47 Super Bowls in which rooting interest is determined by birth order.
Little brothers in red and gold. Big brothers in purple and black.
"This guy I know told me a story about beating the crap out of his older brother," said my brother. "And it was kind of nasty. But it wasn't something he was happy about. He was 15 at the time. The guy is 50 now. Still bothers him I think."
Luckily, that's one thing the Donnellon boys didn't need not worry about.
"What's unique to us is we didn't land a lot," brother Tim said. "We'd have some nasty-assed fights. But there weren't any visible signs of it afterwards."
John and Jim Harbaugh's parents would love that of course, no visible signs. Jackie Harbaugh even joked about how wonderful it would be if they could change the rules for Sunday's game allowing it to end as a tie. She was "comatose" watching the brothers coach against each other two Thanksgivings ago, her husband recalled this week. And no matter how it ends, there will be no escaping how they will feel when it ends on Sunday.
"We went down an elevator and opened the door to the Ravens locker room - I mean, the excitement of victory," Jack Harbaugh said. "We've all experienced that excitement of victory - guys jumping up and down, the smile on John's face . . . Then you realize that you're not needed here. They had so much going on for them.
"You walk across the hall, and you went into the 49ers locker room and . . . that look in their eyes, that look of not being successful and coming up short. We opened up a couple doors and finally saw Jim all by himself in this room, just a table and a chair. He was still in his coaching outfit. His head down in his hands. And you looked into his eyes and you realized that this is where you're needed as a parent.
"Every single parent can identify with that. That thrill of victory and the agony of defeat. On Sunday night, we're going to experience both of those great emotions. Our thoughts will be with the one that comes up a little short."
On Twitter: @samdonnellon