Reid, explaining why it took him until the end of January to address the 2011 season, said he wanted to take some time to reflect on all aspects of his team after a disappointing 8-8 record.
"Bottom line is we have to do better," he said.
Reid said he didn't want to make excuses for the 2011 season, but "I'm very optimistic going forward and I feel very good going into next year."
When asked if he felt more pressure to win from owner Jeffrey Lurie in 2012, Reid said "there's no more pressure than there has been."
"That's why we do this. We do this to bring a championship to the city of Philadelphia, to get the ring and that's why players play, that's why coaches coach. And when we go about our business in the offseason that's how we do it and we crank on that. We spend a lot of hours and are involved in it.
"So I understand where he's coming from and I'm right there with him on that. He didn't say anything in there that ruffled my feathers or anything else that I don't completely agree with. And listen, I know that's how the fans feel and I understand that. I completely understand that. And it's a frustration, I understand that. My point is that we're going to bust our tail to get it right, that's where I'm at."
When asked if he thought 2012 is a make-or-break season for him, Reid said he approaches every season that way.
"I think every season you come out as a coach and a player, it's a make-or-break season. That's how you look at it, and if you don't, you're wrong. You've taken the wrong approach," he said.
Besides the addition of Bowles, the rest of the coaches will remain in their same roles, Reid said. The Eagles coach also said he talked to Steve Spagnuolo about joining his staff before the former St. Louis Rams coach agreed to become the New Orleans Saints' defensive coordinator.
"Steve and I are good friends and we talked throughout the season as we do every year. When Steve was released from the Rams I did offer him a spot here to coach, if he needed one, a place to land with open arms," Reid said. "And my feeling was that you can have two great coaches on defense and that's even better than just having Juan himself, so that's about as far as it went there. We didn't talk about titles. We didn't go into any of that."
Still, he's excited about adding Bowles, the former Miami Dolphins secondary coach and interim head coach to his staff. He said Bowles was highly recommended by NFL personnel he has worked with through his career, such as Bill Parcells and Tony Sparano.
Reid said he never really considered replacing Castillo as his defensive coordinator but was excited about the prospect of adding Spagnuolo to his defensive staff. He said he thought Castillo and Spagnuolo "could be dynamite" together.
"I saw us get better," Reid said, when asked about the job Castillo did in 2011. "We had some moving parts on the defensive side, I understood that."
Since his surprising switch to defensive coordinator last season after 13 seasons coaching the offensive linemen, Castillo has been under the microscope in Philadelphia.
Reid said he anticipated it would take some time to bring those moving parts (such as free-agent additions Nnamdi Asomugha, Jason Babin and Cullen Jenkins) on defense together, but he saw "progress," although it took longer than he hoped for the defense to jell.
"You could tell that the players were all-in, and there are some ex-players out there who can vouch for this that normally if there's an issue and if somebody, if the coach doesn't know what he's talking about the players normally voice an opinion," Reid said. "And so the players were all-in and they believed in Juan and the scheme he was doing and I think it ended up working the way we hoped it would work a little earlier and it didn't."
The defense played poorly when the "Dream Team" Eagles started 1-4, but Philadelphia's defense improved as the season went on and finished eighth overall.
Reid also said he's looking forward to quarterback Michael Vick taking part in a full offseason program, something he has not been able to do since taking over as the Eagles' starter because of the lockout last offseason.
"But there are some things he can, specifically, attack this offseason and he's in the right frame of mind to do that," he said. "He's been in constant communication with me since the season's been over and he is ready to go."
Reid said Vick understands that the Eagles need him healthy if they are to achieve their goals. He doesn't expect that Vick will choose not to run the football anymore, but he hopes he will be smart and get out of bounds before taking a big hit.
"I think Michael will tell you this: You look at the last four teams that are playing in the playoffs and all four quarterbacks didn't miss a start," Reid said. "So he's aware of that and he understands how important he is to this football team when he's healthy. And that means as healthy as you can be playing this sport."
Reid said defensive tackle Mike Patterson is "doing very well" following surgery last Friday for a brain AVM. He said doctors expect Patterson to be ready for training camp.
Information from The Associated Press was used in this report.