Still, the first time it happens to you, it's tough. Particularly when it happens in your hometown, in front of your friends and family.
Particularly when it's with the team you grew up rooting for and even dreaming of playing for some day.
"You have to take that out of the equation because of the business we're in," said McDermott, who is entering his second season as the Carolina Panthers' defensive coordinator. "It was a business decision on their part and I respect that they had to make that decision.
“I'm proud of what we accomplished, I really am. We went to the playoffs 2 years in a row. Led the league in turnovers over those 2 years.
“I don't spend a lot of time looking in my rearview mirror, but I'm proud of what we accomplished. And I learned a lot from the experience and from the transition. My hope is that I'm a better person, better father, better husband and better coach because of it."
McDermott isn't bitter. That doesn't mean he agreed with Reid's decision to replace him. But he isn't bitter. He still talks to Reid.
Still considers him a mentor.
"I have nothing but the utmost respect for him," he said.
Down here with the Panthers, McDermott isn't under the intense scrutiny he was in Philadelphia. Jim Johnson's shadow is big, but not that big.
He's running the Panthers' defense for a head coach with a defensive background — former Bears linebacker and Eagles assistant Ron Rivera.
So most of the time, the buck stops with Rivera.
Rivera was on Reid's staff with McDermott for 5 years, serving as the Eagles' linebackers coach from 1999 to 2003. McDermott spent '01 and '02 as a defensive quality control assistant and helped Rivera with the linebackers.
"Ron and I have a great relationship," McDermott said. "I have a great amount of respect and trust in him. He has ideas and things he wants to see [with the defense]. Yet, at the same time, he gives me freedom to do things I believe in. We have a good meeting of the minds and sharing of ideas."
Ravaged by injuries, McDermott's defense struggled last season. He lost his best defensive tackle, Ron Edwards, to a season-ending triceps tear in training camp. Lost his top two linebackers — Jon Beason and Thomas Davis — to season-ending injuries in the first two games of the regular season.
The Panthers finished 28th in total defense, 27th in points allowed, 27th in third-down efficiency and 25th in yards allowed per rush attempt. Their 24 takeaways were the fifth fewest in the NFC. They had just 31 quarterback sacks.
"Sean was handcuffed last year when you look what happened to us [with injuries]," Rivera said. "We lost Edwards, then Beason and Davis. Then we had a different combination of safeties all season based on who was hurt that week. It was really tough on Sean and the defensive coaching staff."
While McDermott's defense struggled, the offense, led by NFL offensive rookie of the year Cam Newton, finished fifth in the league in scoring as the Panthers improved from two wins in 2010 to six last year. If the defense can make similar improvement this season, Rivera thinks the Panthers can compete for a playoff spot.
"If we can maintain and get better as an offense, which I believe we will, and stay healthy and get better defensively, I think we can win a few more games," he said. "I think we can put ourselves in the playoff hunt. That's really our goal."
There is a saying in sports that you never want to be the guy who follows The Guy. You want to be the guy who follows the guy who followed The Guy.
McDermott didn't do a bad job in his 2 years as Johnson's replacement. Yes, he made some mistakes, but his defense led the league in takeaways in 2009-10. Finished a decent 12th in total defense and 14th in points allowed in '10.
In the Eagles' 2010 five-point playoff loss to the Packers, the defense held the eventual Super Bowl champions to 21 points and gave the ball back to the offense in the fourth quarter with more than enough time to drive and score.
But the pressure of following Johnson was constant. Every decision he made, people wondered WWJD? What would Jim do? And Sean knew they were asking it.
Ultimately, Reid decided McDermott needed a change of scenery, where no one would ask WWJD.
"[Getting fired] is always a possibility in this business," said McDermott when asked if he was surprised that Reid let him go. "He felt like he had to go in a different direction. For me and my career, my hope and my desire is that I'm a better coach for it.
“Hopefully, 10 years from now, being where I'd like to be, accomplishing goals I'd like to accomplish, I hope I look back and say that was a turning point in my career for the better."
Having played for Buddy Ryan in Chicago, having coached 5 years in Philadelphia for Johnson, Rivera knows the immense difficulty McDermott faced replacing one of the best defensive coaches in the history of the game.
"Following somebody who has had a lot of success, the expectations are almost unfair," Rivera said. "When I was playing for the Bears, Vince Tobin came in and replaced Buddy after he left [to become the Eagles' head coach]. Vince never got the respect he deserved because it was Buddy this, Buddy that. But when you look at some of the things Vince did, you say, ‘Wow, that's pretty doggone good.'
“So when I look at Sean's situation — and Andy and I talked about it — just the expectation level was so great, Andy thought this would be a great opportunity for Sean to come down here and reinvent who he is."
Contact Paul Domowitch at email@example.com. For more Eagles coverage and opinion, read the Daily News' Eagles blog, Eagletarian, at www.eagletarian.com. Follow him on Twitter at @PDomo.