Chelsea recently purchased a familiar face to strengthen their midfield, former Blues player Nemanja Matić.
Why did they do this? They did this because the 26-year-old Serbian international blossomed and grew into a powerful - yet delicate - fantastic midfielder at Benfica.
After seeing this move, you wonder why they didn't just loan him out in the first place. Well, you could ask many clubs in the Premier League the same question for many players they also let slip through the net. Here, we take a look at a few of them...
One is Juventus' Paul Pogba. The 20-year-old French international has become a key player for the Old Lady, winning the ball back, distributing it and even scoring goals. It's no secret that he is well on his way to becoming a world-class midfielder, but it is hard to believe this is a player that was free to the Italian giants from Manchester United.
He was seemingly unhappy with not being played as much as he should have been and let his contract run down until he was free to leave. Sorry Fergie, but it seems the young lad had a point.
Another key figure to his club is Blackpool winger Tom Ince. The 21-year-old son of Manchester United legend and former Liverpool player Paul, he is currently carrying the Seasiders in the Championship.
A very accomplished attacking midfielder, he has the ability to score prolifically and even set up his teammates. This was a player Liverpool let go for measly money, inserting a 35% sell-on clause in case he did make it big. Either way, this wasn't the best idea as he did go on to fulfil his potential and hasn't stopped yet. Definitely one that got away.
Sticking to the idea of prolific goalscorers, we move on to Liverpool's Daniel Sturridge. It's obvious that this 24-year-old England international has become one of the best strikers in the Premier League, almost matching every appearance with a goal and of course being half of the lethal partnership that is "SAS".
Before his blooming under Brendan Rodgers, Sturridge was a bit-part player for London giants Chelsea. Playing as a winger and not getting as much time on the pitch as he wanted, he was angling for a move away if he couldn't be played more or even in a central role for the Blues.
They instead leaned towards letting him leave for what is looking increasingly more of a bargain £12m. As they say, the rest is now history. With Sturridge setting the odd goal up, being incredibly prolific and even breaking Liverpool records, it is hard to swallow as a Chelsea fan at a time when they have a striker problem.
Finally, one that is slightly more understandable is Real Sociedad's Mexican international Carlos Vela. Spending a total of seven years at Arsenal, it isn't the case that the Gunners didn't give him a chance.
Loan spell after loan spell proved he could only really be an 'okay' player and this was the case until he went on loan to Real Sociedad. Scoring goals in the double-figures and assisting a good amount from the wing, it looked like he had found his place, igniting his move to the Spanish club permanently for just £4m.
Going on to only get better, the 24-year-old has excelled with 20 goals this season in just 30 games, including four goals in a single match - all from the wing.
There are of course many others that have happened and are still to happen. Will it ever get to a point where clubs stop being so trigger happy with letting people go? Or are they just getting reliant on the fact they can bring anyone in already established?
Either way, don't be surprised if you see any of these - Sturridge aside - make a return to England.
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