Klopp is a fantastic manager. He has shown that he can come into teams, help build them into top sides with his brand of rock n roll football and get them challenging for the top honours in the game.
If Liverpool are to continue to be a success under him though, he's going to have to do something he's never done before, and replace an aging squad, reinvigorating a team that has clearly lost what made them so good, and picking up and almost starting again, and that arguably is the hardest job for a manager and obviously Fergie was the master at it.
It's one thing to come in with fresh ideas, get your transfers right, and mould a team while it's all fresh and exciting. It's another thing to know when you need to ditch the players that have done so well in the past, get as equally good transfers, and just manage to keep everyone in the dressing room and around the squad hungry and fresh that might have heard the same voices the past 7 or 8 years, and actually to keep that hunger and drive yourself as a manager to actually want to start that cycle again, and just deal with the mental fatigue of that relentless chase of Pep and City.