'Never go back' is often good advice when it comes to relationships – workplace or otherwise.
Just because things worked out the first time, it doesn't always make sense to try it all again.
But having said that, Chelsea have been pretty good at it in recent years.
The return of both Nemanja Matic and David Luiz to the club after time away, has seen them flourish as much improved players, who were able to hit the ground running.
The latest name mooted for return is Romelu Lukaku – linked with the gap expected to be left by Diego Costa's departure this summer.
But does he fit the bill of what Antonio Conte needs, or is the suggested move clouded in a bit too nostalgic for what could have been first time around?
The evidence suggests going back to Chelsea is no big deal.
It worked for Graeme Le Saux when he did it in 1997, having spent four years at Blackburn Rovers – during which time he won a Premier League title.
In Le Saux's case, he should probably have never been sold in the first place: a move necessitated by a public falling-out with then boss Ian Porterfield.
The departures of Matic and Luiz were far more straightforward issue, however.
The former actually left the club in part exchange for the latter: heading off as a somewhat gangly 22-year-old for Benfica yet to break through to the Chelsea first team.
But when he returned, three Januaries later and with a £21m price tag, he looked like a completely different player.
The sheer bulk acquired, and the physicality added to the Blues' midfield made him an instant hit – and he remains a hugely underrated asset to what is presently the Premier League's most complete team.
Meanwhile, both Luiz' positives and negatives were well known to Chelsea fans when he made his way to Paris Saint-Germain in summer 2014.
He was a player of great ability, but one who could suffer terrible lapses at the worst moments.
The huge £50m fee reported, but probably a bit less, simply could not be refused.
There were misgivings when he returned two summers later, having scored to knock Chelsea out of the Champions League but also part of the Brazil side humiliated by Germany in the World Cup.
But since his return, he has not put a foot wrong: and has been one of the outstanding performers in Conte's 3-4-3.
So what about Lukaku?
Chelsea were definitely interested in him going into last summer, but the deal with Everton never happened.
He never scored for Chelsea but has found his shooting boots elsewhere.
The criticism is he only tends to find the net when the going is good: scoring easily against poor opposition (such as the four he got versus Bournemouth) and adding to a thrashing when the opposition doesn't turn up (4-0 v Manchester City).
An even greater issue in deciding whether or not Lukaku becomes a Chelsea player again is whether or not he has the mental agility and application to follow Conte's demanding system.
Such traits were not especially evident in his first spell with Blues, and Conte knows exactly what he needs out of a player.
Chelsea, then, generally disprove the theory that one should never go back – when it happens there, it tends to work.
But in Lukaku's case, it remains to be seen whether or not he is the right man to continue that ideal.