It is usually the player who calls time on his Manchester United career rather than the manager.
At many other clubs and at Old Trafford before Sir Alex Ferguson, the manager makes the decision, often leaving embitterment and resentment. Many an old professional feels that they could have done another year or two.
Under Ferguson, a player's time usually ends when he asks for a meeting with the manager to discuss his future.
Ferguson will almost always state that he wants him to stay, but he will be honest about the number of future opportunities.
If a player is not promised first-team football then he usually makes the decision to leave.
John O'Shea was in such a position in the close season. The Irish international defender, 30, had been at Old Trafford since he was 17 and played nearly 400 games for United.
He had scored 15 goals, some of them crucial efforts that will be remembered forever by United fans: a last-minute winner against Liverpool in front of the Kop in 2007, the winning goal in the 2009 Champions League semi-final first leg against Arsenal.
Calm and versatile, O'Shea had played across the defence, midfield and occasionally up front as an emergency striker.
He even played a game in the goal against Tottenham Hotspur. Little wonder that Ferguson described O'Shea as a "great professional who never complains".
O'Shea's problem was that he started less than half United's Premier League games in four of his last five seasons.
The Waterford-born defender had enjoyed 12 seasons playing in United's first team and stayed longer at Old Trafford than all the other 10 players in the team in which he made his debut in 1999.
"Time flies when you're having fun, doesn't it?" said O'Shea, who grew up as a Liverpool fan.
"It's great to have played so many times for United and it's something to be really proud of. To be able to say you've made a contribution to some of the success of the club is a great feeling."
Having just turned 30, O'Shea felt he was at his peak and wanted to play more. An intelligent individual who planned to study economics at University College Dublin before football took over, he made a considered decision.
"The last couple of years were a bit more frustrating for me personally because I hadn't been playing as much as I was for the years before," he said.
O'Shea wanted to play more but Ferguson had other ideas about bringing younger defenders such as Chris Smalling and Phil Jones through. He made the decision to leave and there was no shortage of suitors for the player who has played more than 70 times for the Republic of Ireland.
Sunderland seemed a perfect fit. Managed by a former United defender, Steve Bruce, they were a mid-table Premier League club with a big support and top-class facilities. O'Shea could also speak to several of his former United teammates who had made the Stadium of Light their home.
Kieran Richardson and Phil Bardsley had also played with O'Shea in Manchester and three of Sunderland's four defenders in the 2-0 win at Bolton Wanderers on Sunday were former United players.
It helped too that Sunderland did not just want O'Shea from Old Trafford, but his long-time teammate and fellow defender Wes Brown, and Darron Gibson, the midfielder.
Brown, who was in a similar position to O'Shea, decided to leave a few months earlier while Gibson would reject Sunderland, much to the chagrin of Ferguson and Bruce.
Bruce claimed that Brown and O'Shea would bring a "winning mentality" to the club, but it has not quite worked like that: the weekend victory at Bolton was only their second of a season in which they have triumphed just once at home.
O'Shea, who cost £5 million (Dh29.25m), settled well though, after overcoming pre-season injuries. So well that he has been made captain when Lee Cattermole, the regular club captain, has not started.
He is hoping for an upturn in the side's form.
"We have some great players here and a top manager," he said. "We just need a little luck and to start winning and climb up the table."
It won't get any easier. O'Shea returns to Old Trafford on November 5.