The secret is to strengthen when you're on top - but try telling Chelsea that.
The Blues are guilty of doing the exact opposite at times in recent years and have been forced to regret selling Romelu Lukaku to Everton instead of keeping him at Stamford Bridge to play alongside - or instead of - Diego Costa.
Currently second in the Premier League scoring charts and only two behind Leicester City's Jamie Vardy, the Belgian powerhouse has established himself a proven goalscorer.
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After scoring his 50th goal in England's top flight last November, he became only the fifth player to do so before the age of 23, following in the footsteps of Robbie Fowler, Michael Owen, Cristiano Ronaldo and Wayne Rooney.
Brought to Chelsea in 2011 by then-manager Andre Villas-Boas for around £18 million, the Belgium international was sent out on loan to West Brom and Everton as the west Londoners sought to find the ideal replacement for club legend, Didier Drogba.
And through it all, knowing he was capable of filling that void, Lukaku continued to find the net and learn his craft on loan, fired up by a burning sensation of injustice.
Two-time manager Jose Mourinho eventually sanctioned his unprecedented move to Goodison Park in 2014, raising serious question marks over the Portuguese's judgement - and rightly so.
Indeed, Chelsea's loss has become Everton's resounding gain, even despite the former winning the Premier League after shipping Lukaku.
"He is a striker who can do it all," said manager Roberto Martinez earlier this season.
"He has the old fashioned traits - he can have his back to play, the strength, the power. But he can also run with the ball and is a clinical finisher."
Chelsea ultimately missed out on a striker with exceptional ability and mentality; one that wants to see his goals transpire into trophies.
Even during his time at West Brom, Lukaku revealed he wanted to stay with the Baggies and guide them to success, rather than return to Stamford Bridge: "I'm scoring more goals but we’re not winning.
"You play to win and if we don’t win but I score it doesn’t matter. I want to score goals that win us games.
"Every day is a new opportunity to improve. I’m not wasting my time. I’m taking the maximum out of it."
Chelsea were criticised for not strengthening as seen fit last summer, yet it all could have been so different had they just kept hold of Lukaku the year previous. One that certainly got away for the Blues, and it could soon come back to bite them even more.
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