Chelsea are still mocked for letting future Premier League superstars Kevin De Bruyne and Mohamed Salah walk right out the door.
But in another world perhaps it's Tottenham who could have made the same grave mistake, with Luka Modric initially struggling to settle at the club after his move from Dinamo Zagreb in 2008.
Modric arrived in a £16.5million deal as Spurs beat the likes of Manchester City and Newcastle to the highly-touted Croatian's signature.
However, six losses in the opening eight games of Tottenham's 2008/09 Premier League season may have had Modric wondering if he had made a grave mistake in moving to England.
Juande Ramos, the manager who brought Modric to the club, was sacked in October and replaced by Harry Redknapp.
At first, Redknapp deployed Modric out on the left flank before transitioning him into a central midfield role.
Modric would end his debut Premier League season with ten assists as Tottenham finished eighth.
But Jake Livermore, who was on the fringes of Tottenham's first-team as a budding academy prospect when Modric first arrived, knew the club had a gem on their hands.
All the Croatian needed was time.
"I'm not sure about that [Modric leaving], but sometimes players like that, they need the rest of the players to bounce off of them," Livermore said in an exclusive interview with talkSPORT.
"I think maybe in his first season he struggled because the team didn't realise what he had and I think it soon became apparent after that... we had to give him the ball, feed him the ball and make runs off of him.
"I think once he started to gel with the rest of the team and the rest of the team started to see what he could do, I think then he obviously came into his own."
As they say, the rest is history.
Modric went on to establish himself as one of the Premier League's best central midfielders and helped Tottenham to their best league finish in 20 years.
The Croatian's sparkling form attracted interest from Europe's biggest clubs and prompted Real Madrid to part with £30m to sign Modric in 2012.
It proved to be an incredibly shrewd acquisition.
With Modric bossing their midfield, Madrid have won the Champions League a staggering six times.
Modric even beat out Lionel Messi and Cristiano Ronaldo to football's top individual gong, the Ballon d'Or, in 2018.
The Croatian has proved himself to be one of modern footballer's finest midfielders, with Livermore fortunate enough to play with the Croatian 26 times.
Livermore has also lined up alongside other electric talents to come through at Tottenham, including Gareth Bale and Harry Kane.
Bale became a teammate of Modric once again when he joined Madrid in 2013 for an eye-watering £85m, while Kane stands alone as Tottenham's all-time leading goalscorer.
Safe to say, all three have gone on to reach incredible highs in football, albeit Kane has been rather luckless in his pursuit of a team trophy.
Yet there's only one name out of the trio that stands out for Livermore as the best he played alongside.
"I think being a midfielder myself, Luka Modric is probably the pick of the bunch for me," he said.
"Gareth was immense for a couple of seasons, two in particular. Everything he hit just turned to gold.
"But I think being a midfielder myself and playing alongside him and trying to learn from him, I think Modric is probably the pick of the bunch for me."
At the age of 39, Modric remains a key part of Madrid's midfield despite the arrivals of Aurelian Tchouameni, Eduardo Camavinga and Jude Bellingham in recent seasons.
Modric, Madrid's captain, has started five LaLiga games for Los Blancos this season and has one assist to his name.
It could be his last campaign in the iconic white shirt as his contract expires in June next year, but he and Los Blancos will hope he has a golden send-off with even more glory.