Short of displays of match-winning brilliance, few things elevate a footballer's standing like his absence when setbacks are suffered. Suddenly his attributes are apparent, his presence pivotal. Those who are sidelined for long periods can return with a sky-high reputation that can only be diminished by actually playing.
But there is a separate group, of players whose status grows by the game at the place where they no longer ply their trade. It is less than a third of the way into the Premier League season, but the evidence is accumulating that several clubs are being made to regret the ones that got away: the players they sold.
If it was blindingly obvious that, however Olivier Giroud and Lukas Podolski fared, Arsenal would find Robin van Persie hard to replace after 30 league goals and a further nine assists in a campaign that earned him both major Footballer of the Year awards, others slipped out of the back door comparatively quietly. Football's fascination with the new means arrivals usually attract more attention than those who depart, but the latter can be more significant.
Arguably Manchester City found not one but two successors to Nigel de Jong, bringing in first Jack Rodwell and then Javi Garcia. They cost a combined £27 million, while the Premier League champions only recouped an initial £3.5 million when De Jong joined AC Milan. It is not just the financial figures that suggest City ended up poorer for their midfield trading.
Rodwell's major contribution to City's season so far has been an awful pass to enable Marco Reus to give Borussia Dortmund the lead in September's Champions League meeting, while Garcia was hauled off at half-time in last week's draw with Ajax and was not required at all for Sunday's win over Tottenham.
If he, like De Jong last season, finds himself behind Gareth Barry in the queue for midfield places, the context has changed. The Dutchman spent much of last season on the bench, but City were defensively excellent. Now, with clean sheets more of a rarity and a back four left exposed all too often, the man who was the foremost defensive midfielder in the Premier League in the 2010-11 campaign could have come in handy.
Chelsea, too, find themselves short at the base of the midfield. The English transfer window had slammed shut before Raul Meireles was offloaded to Fenerbahce, almost as an afterthought. Meireles' moves are becoming an annual affair but, for the second successive season, the sellers may end up regretting casting him aside.
While the European champions are overwhelmed with progressive talents after the summer signings of four wingers or playmakers, they are rather more short-staffed further back, especially as Frank Lampard is injured and Roberto Di Matteo does not appear to trust Oriol Romeu. John Obi Mikel and Ramires risk being overworked and, while there are times when Chelsea could benefit from the Brazilian's energetic presence on the right wing, a lack of alternatives deeper in the midfield means Di Matteo cannot field him there. So their course is set to attack and their defence left more exposed.
Meireles' former employers, Liverpool, have been castigated for offloading Andy Carroll without bringing in reinforcements. More significant, arguably, were the exits of Dirk Kuyt, Maxi Rodriguez and Craig Bellamy. None were Brendan Rodgers' fault but, even in a season when they were selected too rarely and which was the Dutch forward's most barren at Anfield, they still contributed 20 goals between them in the last campaign. Given the current reliance on Luis Suarez and the suspicion that Rodriguez would have suited Rodgers' style of football, the Argentine is a particular miss.
Tottenham, too, have cause to pine for a midfielder with a clinical touch. In Clint Dempsey and Gylfi Sigurdsson, they thought they had acquired two. However, Spurs have struggled to secure victories at White Hart Lane, where neither has scored but where Rafael van der Vaart's unpredictability was an asset. The Hamburg player's reluctance to track back may have made him ill-suited to Andre Villas-Boas' gameplan and away games alike, but he has a priceless capacity to make things happen.
If Manchester United's run of 16 wins in 18 games suggests few flaws in Sir Alex Ferguson's transfer dealings, they have reasons to regret letting Fabio da Silva go on loan to QPR. The full-back has been sidelined at Loftus Road, but that does not necessarily mean he would have been unfit at Old Trafford. And, during Ferguson's annual defensive injury crisis, Fabio may have spared his brother Rafael and Patrice Evra, two of United's busiest players, some time on the pitch. As it was, the Frenchman's unconvincing deputy, Alexander Buttner, was taken off at half-time in the Capital One Cup loss to Chelsea. Fabio may have only been on the margins of the team, but United have been short of fringe players with first-team experience in the back four.
Hindsight is a famously wonderful thing and issues from diplomacy to pride often prevent managers admitting they, or their club, have erred. But there is the sense that some did not appreciate what they had until it was too late, because certain players have never been more crucial now they are no longer around.