Lots of players leave Chelsea, but Nathaniel Chalobah's move to Watford last week stung Blues supporters a lot more than most.
Having joined Chelsea's academy at the age of 10, grown up at Cobham and navigated a turbulent journey through six different loan clubs, Chalobah took a significant step forward last season by establishing himself on the fringe of the first-team squad.
Antonio Conte was impressed, but his trust only extended as far as one Premier League start and nine substitute appearances. At 22, Chalobah needed more and his departure, while painful for all parties, was necessary. "Maybe now is not the right time but I'm sure our paths will cross again," he wrote on Instagram.
That scenario is made more likely by the fact that just as with Bertrand Traore's move to Lyon and Nathan Ake's transfer to Bournemouth earlier this summer, Chelsea succeeded in negotiating a buy-back clause in the deal that took Chalobah to Watford, sources have told ESPN FC.
The agreed prices and precise conditions of the clauses remain undisclosed, but the mere fact that they exist suggests we may be witnessing a significant change in Chelsea's approach to player development.
Chelsea have dabbled with buy-back clauses; they passed on a time-sensitive option to re-sign Thorgan Hazard from Borussia Monchengladbach for £13 million in 2016, while an opportunity to return to Stamford Bridge was included in the permanent deal that took Josh McEachran to Brentford two years ago.
But these were exceptions rather than the rule, and more often the Premier League champions have been left to regret their short-sightedness when selling talented young players desperate for first-team minutes.
Romelu Lukaku and Kevin De Bruyne, both undervalued and mismanaged by Jose Mourinho, might well be Chelsea players now if deals that took them to Everton and Wolfsburg, respectively, had been structured with an eye towards their future development.
Ryan Bertrand, now an established England international, might have saved Roman Abramovich a lot of money on left-sided defenders if a path back from Southampton to Stamford Bridge had been clearly defined. Mohamed Salah could become another name to add to the list if he brings his Roma form to Liverpool.
Loans have been Chelsea's primary method of managing player development in Michael Emenalo's time as technical director. More than 30 players have been sent out every year since 2012, with particularly close ties forged to Vitesse in the Netherlands and Sint-Truidense in Belgium.
As a system it is as clever as it is controversial, a vast bank of relatively low-cost assets that almost universally increase in value year-on-year, and that can either be recalled, sold off or loaned again as circumstances require.
But from a development perspective, loans are tricky. It's difficult to effectively incentivise loan clubs -- particularly those with Premier League or Championship resources -- to consistently select the players they are given. Even if a manager promises to give a youngster the desired opportunities, there is no guarantee he won't be sacked and replaced by a different coach with other ideas.
Loan players often have to overcome the perception that they're just passing through when they arrive at their temporary clubs, and the nature of the agreement means their commitment can be questioned more easily. Selling with an option to buy back grants enough stability to minimise that issue.
Being constantly shunted to different clubs and countries can also be demoralising, as young footballers with the talent to establish themselves are instead consigned to the lifestyle of a journeyman.
"I'm tired of moving abroad," a disillusioned Lucas Piazon told the Daily Mail in September 2016. "One, two, three loans, maybe that's enough. It's time for me to stay somewhere more than one year. When they know you'll stay whatever happens, people look at you with different eyes."
Permanent deals suit the purchasing club and the player, but the selling club also benefits. They recoup a transfer fee (though admittedly slightly less than might be negotiated without the buy-back clause), while insuring themselves against the possibility of the player maturing into a star who could strengthen a rival.
If the selling club is smart, they can also set up a great value deal down the line. Real Madrid paid just £23m to bring back Alvaro Morata from Juventus in the summer of 2016, and now price him at around £70m.
That is an extreme example, but both Madrid (Morata, Dani Carvajal) and Barcelona (Denis Suarez, Gerard Deulofeu) have regularly insisted on buy-back clauses and utilised them intelligently in recent years.
Chelsea's delay in following suit has already cost them, but should this summer prove a sign of things to come, there is no reason why the likes of Chalobah, Ake and Traore need go the same way as Lukaku, De Bruyne and Bertrand if they begin to fulfill their considerable potential elsewhere.