As someone who’s been watching Mark Harmon since the early St. Elsewhere days (and of course, NCIS), there’s always been something steady about him. In his latest PEOPLE interview, he gave a hint at why: it comes down to a piece of advice from his dad—simple, direct, and still guiding him decades later.

“If it’s not true, don’t worry about it,” Harmon said.

It’s the kind of thing you can picture Gibbs himself saying, only quieter and with that half-smile fans know so well.

Raised on Work, Not Shortcuts

Harmon grew up in Burbank, the youngest of three, with a Heisman Trophy-winning father, Tom Harmon, and an artist mother, Elyse Knox. Those values of effort and showing up stuck, even when Mark swapped football fields for film sets.

“I’m a practice guy… you tell me I can’t do something, I’m probably going to prove you wrong,” he said.

Long-time fans will tell you that’s exactly why his Gibbs never felt like a performance—it was grounded in how Harmon actually approaches life: no flash, just focus.

Carrying His Dad’s Words

Harmon lost his father when he was 38, but the advice stayed: work hard, treat people with kindness, and don’t let fame change you.

“Work your ass off, and don’t let the effort show. Treat people the same, not based on who they are or what they are,” he said.

Anyone who’s watched him over the years—quietly stepping back from the spotlight even while leading NCIS to insane ratings—knows he’s kept that promise.

A Career Built on Preparation

After a short run as UCLA’s quarterback, Harmon stepped into acting—and never really looked back. By the time NCIS rolled around, he was more than ready, which might be why his Gibbs felt lived in from day one.

“Your job is to be prepared for the opportunity—it will come, you just won’t know when. Until then, all you can do is invest in yourself.”

If you’ve followed him through Chicago Hope, the West Wing arc, and then NCIS, you know this isn’t just talk. Harmon shows up—always has.

Married to actress Pam Dawber for more than 30 years, dad to two sons, Harmon has always drawn a line between his work and home life. Even that old Sexiest Man Alive title? He laughed it off then and still does now, more amused than flattered.

And maybe that’s the secret. Fame never swallowed him whole because he never let it.

Why Fans Still Connect

Fans like me keep watching because Harmon doesn’t play at being grounded—he is grounded. You can feel it, whether it’s Gibbs giving Abby that silent nod of trust or Mark Harmon, the actor, stepping back from the spotlight when it was time.

“I’m a lucky guy,” he said, “but you earn luck.”

It’s that mix of humility and quiet confidence that keeps him one of TV’s rare steady figures. No drama, no fuss—just a guy who took his dad’s advice and built a life out of it.