For the most part, elite-level players know that football has become a squad game.
With teams playing as many as 50 or 60 games in a season, it has to be. Unless you're Cristiano Ronaldo or Lionel Messi, you're unlikely to play every week.
Even David De Gea, a goalkeeper, was rested by Manchester United at Newcastle earlier this month.
But for managers, it's a balancing act. Give a player too many games, and they'll burn out. Too few, and they'll become restless and frustrated.
Javier Hernandez has every right to be frustrated.
A little more than three years ago, the Mexican striker was starting a Champions League final against Barcelona at Wembley. This season, he has started just five games in the Premier League. Eleven in all competitions.
Under David Moyes, he has become United's fourth-choice striker. Robin van Persie hasn't played since the middle of March after suffering a knee injury that might yet end his season.
But since Van Persie was sidelined, Hernandez has started just once, at Newcastle a fortnight ago. For the record, he scored.
He scored in the 4-1 win over Aston Villa at Old Trafford as well. But his celebration, a stern stare into the Stretford End, will have worried some United fans.
The huge smile that usually accompanies his goals was missing. His feelings wouldn't have been made any more clear if he had lifted up his shirt to reveal the message, "I'm not happy."
It's not all Moyes' fault. Hernandez's strengths are his pace and his finishing ability. He likes running in behind defenders and poaching in the penalty area.
He's not Wayne Rooney, who doesn't mind dropping deep to involve himself in the game.
Hernandez's stature makes it hard for him to lead the line on his own, something Moyes has asked his strikers to do often this season.
But he is the perfect substitute. There are few players in the world you'd rather turn to if you needed a goal in the last 15 minutes. And it's no coincidence that only Ole Gunnar Solskjaer, the most famous super sub, has scored more goals for United off the bench.
But sitting on the bench waiting for his chance won't quench Hernandez's desire for more games. At 25 years old, it's understandable that he wants to play more. There would be something wrong if he didn't.
So for now at least, the ball is in Moyes' court.
Hernandez still has a contract at Old Trafford. And if United don't want to let him go, they don't have to. But Hernandez won't be satisfied until he's more involved.
And if Moyes wants to keep him, he'll be forced to find a better way to juggle his squad.
Hernandez's situation is an unusual one. He's a vital part of United's squad but not necessarily as a regular starter.
His ability to change games as a substitute is a rare and valuable quality—one that Moyes will find very hard to replace if Hernandez leaves.
Moyes can solve the problem by giving Hernandez more responsibility next season. But if he doesn't, United's squad will be weaker for it.