Building a football team is a tricky business.
To be successful, you first need good players. Then you need to use them in the positions that best suit their ability. Then you need a system that includes 11 good players playing in positions that allow them to be good.
Do that, and you're onto a winner.
The point is that having 11 good players isn't enough. Lionel Messi is one of the best players in the world, but a team filled with 11 Messi's is unlikely to win very often—although the entertainment value would probably be worth it.
Messi, as good as he is, is unlikely to put in a dazzling show at right-back or at centre-half. He's a forward and, at Barcelona, is utilised as such.
But it raises the question, is a good player still a good player even when he's played out of position?
It would be interesting to hear Shinji Kagawa's opinion.
It was Kagawa's performances as a No.10 that convinced Sir Alex Ferguson to splash more than £12m on the Japanese midfielder in 2012. But since arriving at Old Trafford, he's been predominantly used on the left.
Jurgen Klopp, Kagawa's coach at Borussia Dortmund, admitted to crying at seeing him played out of position at Manchester United last season. It has continued this season under new manager David Moyes.
To some extent, he has been a victim of circumstance.
It was assumed on his arrival that he would fill the desperate need for a creative midfielder at United. He would, it was thought, play behind Wayne Rooney, delivering the same kind of service as he had for Robert Lewandowski at Dortmund.
Then came Robin van Persie, a player so good who Ferguson couldn't resist. In that moment, the pecking order changed. Rooney was to play behind or alongside Van Persie, with Kagawa left over to be shoehorned in elsewhere and triggering Klopp's tears.
While Rooney and Van Persie remain, it's unlikely Kagawa will escape from the left. It's better than being sat on the bench, but it's still not his best position.
Assuming that Moyes has no desire to oust either of his two star strikers for the benefit of Kagawa, the 24-year-old is destined for another season on the wing.
And with it comes the question, is Kagawa still Kagawa when he's played on the left? The answer, according to Klopp at least, is no.
It's led to stories of a swap deal involving Dortmund's Marco Reus.
Most United fans would hate to see Kagawa leave. Were he to move on in January, they will never have seen him at his best.
They've had glimpses of what he can do as a No.10 in two games against Real Sociedad, but it was only a tantalising taste of his talent.
Moyes, though, has a team to build. There might not be many better No.10s than Kagawa, but that, if his first three months in change are anything to go by, is not what the United manager needs.
There are, however, better left-sided midfielders, and if Moyes sees that as Kagawa's long-term role, then he would be better off signing a player more suited to it.
Kagawa's talent isn't in doubt. But the opportunity to showcase it at United is.
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