Sir Alex Ferguson, the former Manchester United manager who would become the most successful British coach in history, realised there was no room for sentiment in football.
As soon as a player showed the slightest signs of decline, it was time to move them on once a suitable, younger replacement had been identified.
No matter how much the Manchester United supporters loved the players in question, Ferguson always did what he felt was best for the team.
Perhaps it was harsh on the players involved at times, especially if they had given years of committed service, but had Ferguson failed to react at these crucial moments then he would not have been performing his duties as a responsible manager.
Ferguson's successor David Moyes will face a host of similar dilemmas over the forthcoming months and years - and he'll be judged on the success of his decision making.
For around 18 months now, the Red Devils have been keeping close tabs on Borussia Dortmund striker Robert Lewandowski, whose contract expires at the end of the season.
Ferguson was, and no doubt still is, a keen admirer of the Poland international - as are most of Europe's top clubs.
While Bayern Munich were expected to sign the prolific 25-year-old, recent reports suggest that the interested Premier League clubs - including Arsenal, Chelsea and Manchester United - all stand a half-decent chance of luring him to England in January.
Like Lewandowski's former teammate Shinji Kagawa, the Dortmund star would jump at the chance to play for a club as prestigious as Manchester United if the offer was right.
He would obviously need assurances, which is the only barrier stopping Manchester United from making a bid in January.
But Moyes should ask himself the following questions: in the long run, will I benefit more from having a mid-20s Lewandowski or an early-30s Van Persie in my team?
Is Van Persie capable of ever producing the same sublime form as he did last season at Old Trafford? Will Lewandowski become the world's best No. 9 in a few years' time - when Van Persie is 32, 33?
In terms of current ability, there's little to separate the two strikers. They're both top-quality forwards. But in terms of potential there's no comparison: we've already seen the very best of Robin van Persie, who will continue to perform at a very high level but will not improve as a dynamic striker in the same way Lewandowski will.
Despite the fact Ferguson splashed out £24.5m on Van Persie last season, it makes perfect sense to at least try to secure the signing of Lewandowski, who could enjoy his peak years at Old Trafford.
Perhaps Moyes could think of a way to fit Lewandowski, Van Persie and Wayne Rooney into the system.
But if he can't, the Manchester United boss must do what's right for Manchester United.