When David Moyes agreed to succeed Sir Alex Ferguson at Manchester United, he accepted challenges on and off the pitch.
The size of the task on the pitch is obvious.
Ferguson won 13 Premier League titles, five FA Cups, four League Cups, the Champions League twice and everything else in between in 26 years at Old Trafford.
It's Moyes' unenviable job to carry that on.
But off the pitch, Moyes faces a different challenge: to earn the respect of a dressing room full of world-class players and, on top of that, keep them all happy.
It was one of Ferguson's great achievements that he adapted to changes in the game throughout his long career.
Over the course of the 1987-88 season, Ferguson's first full campaign at Old Trafford, United played 48 games.
In 1998-99, they played 63 games and won the treble, a feat only made possible because Ferguson had built a large squad capable of dealing with the rigours of three competitions.
His list of substitutes that night in the Nou Camp read Raimond van der Gouw, Wes Brown, David May, Jonathan Greening, Phil Neville, Ole Gunnar Solskjaer and Teddy Sheringham.
Nicky Butt and Jesper Blomqvist would have been on there, too, had Roy Keane and Paul Scholes not been suspended. Henning Berg missed out because of injury.
Those players were all good enough to hold down regular places elsewhere. But they stayed because Ferguson managed to keep everyone smiling and motivated.
Moyes has to do the same.
Javier Hernandez is one who sounds like he could do with an arm round his shoulder.
After starting just twice this season, the Mexican striker, who's under contract until 2016, has revealed he's desperate for more playing time, hinting that he could go elsewhere to find it.
But Hernandez, United's second highest-scoring substitute behind Solskjaer, is exactly the type of player Moyes needs to keep hold of.
Able to turn a game off the bench as fast as he is over 100 yards, he's the perfect squad player.
And in the age of 60-game seasons, that's a valuable commodity.
Moyes' powers of persuasion will be put to the test with Hernandez, who could expect to walk into most teams in the Premier League, as they will be with Adnan Januzaj.
They are very different cases, but Januzaj is yet to be convinced that Old Trafford is the best place for him, too.
Januzaj is different because he may yet become a first-team regular at United. But not yet.
Moyes' job between now and the end of the season, when Januzaj's contract expires, is to convince the 18-year-old that in the years between exciting prospect and superstar, he'll get plenty of opportunities if he keeps working hard.
Hernandez and Januzaj will give Moyes his first real test at the delicate man-management involved at the world's biggest clubs.
Where a room full of superstars all want to feel loved and a pat on the head comes in the form of a Premier League start.