Gerard Pique, who can lay claim to being the best defender in the world, left Manchester United because of a lack of first-team action in 2008. Much as he admired the players ahead of him, the Catalan felt that he would have no chance of breaking the seemingly impenetrable central partnership of Rio Ferdinand and Nemanja Vidic.
"They are two of the best centre-backs in the world and probably the best central defensive partnership in the world, certainly a reason United don't concede many goals," Pique said in his last season.
"Rio is technically better on the ball, a leader of the team who always talks. He is deceivingly strong - I see that in the gym at Carrington, but on the pitch he'll get closer to strikers to stop them turning whereas Vida is more aggressive. He sees every game as a battle in which he must win. Vida is solid. You would fancy him to win any 50/50 ball. You would still fancy him if two opposing players went for the same ball as him."
Pique's decision to move back to his hometown club was understandable. He has not come close to regretting that decision.
The phrase "defence wins championships" is oft-uttered in American sport and United's defence has been the bedrock of so many of their championship wining sides.
With Ferdinand and Vidic at its heart, it only improved. United conceded more than 30 goals in Sir Alex Ferguson's first eight title-winning seasons at the club up to 2007. With Vidic and Ferdinand established, the defence conceded just 24, 22 and 27 goals in subsequent wins. Even when United finished second in 2010, the red defence conceded only 28 goals.
United won the league again last season, but with injury restricting Ferdinand to 29 starts - 18 fewer than his replacement as captain Vidic - United conceded a relatively profligate and very surprising 37 goals.
Fulham, in eighth place, had a better away defensive record than United. Wigan Athletic, in 17th, conceded only two more goals than the champions.
Ferguson felt that he needed to make changes in the summer and let the veteran defenders John O'Shea and Wes Brown leave. Both over 30; they were not the future. Pique, sadly, had long since gone.
United bought Chris Smalling, then 20 and just 13 appearances into a Fulham career, for £10 million (Dh58m) in 2010. Ferguson repeated the tactic in 2011 with the £16.5m signing of Phil Jones, 19. He had made 35 just appearances for Blackburn Rovers.
As with Smalling, fans were underwhelmed. As with Smalling, Jones has been an unquestionable success.
The versatile pair have been called up for the full England squad and could play together for club and country for a decade.
Ferdinand, 32, and Vidic, who turns 30 next month, started the first league game at West Bromwich Albion in August, with Smalling at right-back. Vidic and Ferdinand left the field due to injuries in the second half with the score at 1-1. They were replaced, to much nervousness among the 3,000 travelling fans, by Jones and Jonny Evans.
United got a late winner and so the template was set for the season, with Jones, Smalling and a much improved Evans, 23, all vital to United's fine start.
Fans would have been uncomfortable at the prospect of a United defence without Vidic and Ferdinand for last Wednesday's away trip to Benfica. But, such has been their impact, they are at ease with their new defenders. They coped admirably with Benfica's thrusting attacks.
United have conceded three goals in four league games so far - two of them in the 8-2 victory over Arsenal with Smalling and especially Jones becoming cult heroes among the Old Trafford crowd.
With Ferdinand back in contention to face Chelsea today, Ferguson is spoilt for choice in defence. History might dictate that a solid central defensive partnership wins leagues, but it is implausible that Jones and Smalling will not feature more regularly this season.
If they don't, there is always the risk that they will leave, eventually. United lost a world-class defender in Pique. It is unlikely that Ferguson will let it happen again.