Players aren't bigger than the clubs hence they can leave and the clubs continue to be winning. There's some players I can say they're holding the team backwards because they're the vocal point of attack by the club and other players don't get the opportunity to become important because there's already someone that the manager and club owners wants to succeed. No player can play more than Messi, Ronaldo when they're in a team. Everybody will be playing for them to get all the glory hence they get to hold the team backwards sometimes. It's only the playing pattern by the player that's going to to be missed but he can be replaced in the same window that he leaves or in the future when other talents are being discovered. No manager should make a player feel he's too important to not be sold before it gets into their head and they begin to ask for outrageous salaries and put on arrogant behaviours.