Perhaps the biggest pitfall of signing players is that a club doesn’t quite know what they are like. Yes, it can analyze the data, perform various medical tests, watch video after video, but who are they, really? Will they adjust to a new life in a new city? Will they get on with their teammates and the coaching staff? Will their skills integrate into the system? No matter how much research a club does, there is always an element of the unknown. All of which makes it even odder that two of the biggest moves this summer transfer window will involve players leaving clubs to which they had returned for a second go-around, as Romelu Lukaku gets set to depart Chelsea on loan to go back to Inter Milan and Paul Pogba moves on from Manchester United to Juventus, also for a second time.