He couldn't survive the loss of Peyton Manning.
Caldwell became the Colts' third high-profile dismissal in an off-season purge, getting fired Tuesday after producing the franchise's worst record in two decades.
"This is obviously a big transitional time for us, and I know we're excited moving forward and it's hard when you say goodbyes to some people," team owner Jim Irsay said. "But it's part of the business."
In Indianapolis, it's been anything but business as usual.
The day after they finished 2-14 and locked up the No. 1 overall draft pick, Irsay fired team vice chairman Bill Polian, the architect of the Colts' success, and his son, Chris, the hand-picked general manager.
A nine-day search prompted Irsay to hire 39-year-old Ryan Grigson as the replacement last Wednesday.
Since then, Irsay and his new GM have been meeting almost non-stop, debating what tack the team needed to take next — bringing in new assistants to fix the problems or making wholesale changes?
Things were so clouded Monday that Caldwell even met with former Rams coach Steve Spagnuolo about possibly becoming the Colts' new defensive co-ordinator. By Tuesday morning, the conventional wisdom in Indy and around league circles was that Caldwell would return.
A few hours later, everything changed as suddenly as the Colts' 2011 fortunes. Irsay said he informed Caldwell of the decision shortly before the team confirmed the move. The search for a new coach is to begin immediately though neither Irsay nor Grigson provided a timeline for the hiring.
"We just came to the conclusion that this is best moving forward for the franchise," Grigson said, referring to his first major decision in charge of an NFL team. "Mr. Irsay is the steward of this franchise and I'm here to help him wrap his head around these types of decisions. We've been in football our whole lives and a lot of it is about instincts."
It's also about results, and Caldwell's were mixed.
After winning his first 14 games, an NFL record for a rookie head coach, and becoming only the fifth first-year coach to take his team to the Super Bowl, Caldwell did a masterful job guiding the injury-plagued Colts through a plague of injuries and back to the playoffs in 2010.
But those successes all came with Manning, who led the Colts to a league-record 115 regular-season wins in the previous decade and a record-tying nine straight playoff appearances.
This season, without the franchise quarterback behind centre, the Colts lost their first 13 games before winning twice in five days.
Among players and coaches, Caldwell was universally well-liked. The list included Manning, who won all four of his record-setting MVP Awards with Caldwell on Indy's staff, as well as perennial Pro Bowl centre Jeff Saturday.
"I think coach Caldwell has done a very good job. He has gotten the most out of his players, and we play hard for him each and every week," Saturday said before the season finale. "We haven't necessarily played well, we've made mistakes and done things, but they have, oftentimes, been things that we've talked about in coaching meetings."
Outsiders often saw it another way.
Fans frequently complained about Caldwell's game management, and some critics referred to Caldwell as a "puppet" of the Polians.
Many never forgave Caldwell for pulling the plug on a perfect season in a Game 15 loss to the Jets in 2009 and pointed to the midseason firing of defensive co-ordinator Larry Coyer and the long delay in replacing Curtis Painter with Dan Orlvosky at quarterback as decisions that should have come much earlier.
Irsay and Grigson did not characterize Caldwell's 1,099-day tenure the same way fans did, though it sounded as if they agreed with some points.
"We want leadership. Leadership is important," Grigson said when asked about the characteristics he sought in a new coach. "We want strong leadership, and we want someone who shares his vision in this new era of Colts football. We want the best man and the best leader and the man that gives us the best way to go."
Though it's unclear who the Colts may target, the possibilities could include Green Bay offensive co-ordinator Joe Philbin, Eagles offensive co-ordinator Marty Morhinweg and perhaps Spagnuolo.
The last time Irsay presided over such a massive housecleaning was after the 1997 season when he replaced Bill Tobin with Bill Polian, coach Lindy Infante with Jim Mora and quarterback Jim Harbaugh with Manning.
It could happen again.
With Grigson, the new GM, already searching for a new coach and presumably preparing to take Andrew Luck with the No. 1 pick, the questions now turn to Manning, whose future has been unclear since having his third neck surgery in 19 months on Sept. 8.
The Colts still are not saying much about Manning's recovery, and Grigson has not yet spoken with Manning.
"We're not even there with anything regarding Peyton Manning just yet," Grigson said. "We have to know about his medical stuff, first. There's so many things there."
Caldwell ends his Colts' tenure 26-22 overall with one AFC title, two division crowns and one bleak season that has left him unemployed just three years after replacing close friend Tony Dungy, the first black coach to hoist the Lombardi Trophy.
"This was a difficult decision," Irsay said. "I wanted to make sure we took all the time we needed to make sure it was the right decision. ... And just like 14 years, ago, it's a big change for the franchise and at the same time, there's players, coaches, many people on the staff that will go into the new day and get on with the work of 2012."