When Manchester United sold Cristiano Ronaldo for £80 million to Real Madrid in the summer of 2009, many had suggested that it was a deal that suited everyone involved.
Real got their player, the player got his dream move and the Red Devils received a world record transfer fee for their star man.
At the time, the deal was perhaps the right thing to do - United would have been on to a losing battle had they had stood in Ronaldo's way.
But, since his departure, the Old Trafford outfit have never recovered and this is down to a combination of a number of things.
The first is that the Red Devils never replaced the Portuguese star.
However, in all honesty, Ronaldo was always going to be irreplaceable. The only player United could have really signed to replace him was Lionel Messi - and that was impossible.
United were always going to be weakened when their star player left. His brilliance and quality lit up the Old Trafford stage for a number of years and his presence on the pitch was always going to be missed.
Ronaldo's departure from Manchester came just after the Red Devils made it to back-to-back Champions League finals - and despite getting to the final in 2011, United have not been the same force in Europe since.
Additionally, the summer he left, United had just won three Premier League titles on the bounce.
United have won two in four league championships since - still an impressive achievement - but that complete dominance has gone.
There's no doubt that the Red Devils have still been successful, but from what they were - with Ronaldo - they've unquestionably lost their greatest spark.
But, this was always going to be the case, Ronaldo has arguably been one of the greatest ever players to live - to put him in or take him away from any side would make a major difference.
However, United did make an error. As already mentioned, to replace Ronaldo was always going to be extremely difficult.
But, when they lost their superstar, they had to find a world-class, in the Ronaldo position, to keep United in the driving seat.
They didn't and still haven't.
The summer the Portuguese star left was the same summer Antonio Valencia signed, but did anyone ever expect him to have anywhere near the same impact as Ronaldo?
Michael Owen signed the same summer and was given Ronaldo's No.7 shirt at Old Trafford. When he departed the club, Valencia took on the shirt for a season, before handing it back.
And, this season, the No.7 shirt has been vacated. Quite possibly because deep down United players and fans alike still feel the shirt is Ronaldo's.
As it was Beckham's before, and Cantona's before that - only special players can really make the shirt their own.
United now need to find their next special No.7 and then the ghost of Ronaldo will finally depart Old Trafford.