This one is pretty obvious, right?
In what is likely one of the biggest mistakes in the history of the NFL, allowing Tom Brady to walk out of New England when he did will forever bring heartbreak to all Patriots fans.
Without deep diving into all of the glory and greatness that the greatest of all time brought to the Patriots over his twenty years there, the events that led to him leaving New England still rile up fans to this day, even though the accurate details remain a mystery.
There have been several rumors about why Brady chose to leave, with most of the blame being put on Belichick's shoulders for not being willing to pay the legendary quarterback a fair salary.
On top of that, his apparent refusal to spend the money needed in free agency to build a roster around Brady that would elevate the chances of making a deep postseason run is another plausible reason that led to his departure, hence why he chose to sign with the loaded Tampa Bay Buccaneers.
With even Brady somewhat alluding to it himself, it has also been discussed that he was checked out before the 2019 season began and had already decided he was ready to move on.
No matter what is true, it's more likely a combination of factors that collectively forced Brady to depart, and most believe Belichick should have done more to keep him in New England as long as possible.
In his first season with the Bucs, Brady went on to win the Super Bowl against the Kansas City Chiefs, proving if age had been a concern in Belichick's mind, it certainly wasn't a factor. The following year, he led the league in attempted and completed passes, passing yards, and touchdowns, all at 44.
His final season in 2022 didn't end favorably, but the three years he spent outside of Foxboro was evidence that he could still perform at a high level, making it even more unfortunate that he didn't end his career where it began.