"Unlocking Paul Pogba" has become Manchester United's Schrödinger's cat since 2016.
Simultaneously Pogba can be seen as the best midfielder in the world and an overhyped talent failing to reach his potential. If only multiple United managers could find the skeleton key to unlock him we'd get our definitive conclusion.
The £89m midfielder was supposed to be the transformative ingredient that would lead United back to an era of glory and acclaim.
Instead, the Frenchman's second spell at Old Trafford has more been defined by a consistent feeling that the midfielder has flattered to deceive. Brief flashes of excellence followed by longer periods of drift.
Now Pogba sits on the sidelines as his contract ticks down to its expiry with the expectation of his departure.
You almost wonder if this six-year project was worth the hassle. Could that £89m have been better invested during that period? But that's a question you could relate to many of United's signings since Sir Alex Ferguson's departure.
Thomas Tuchel will be hoping to not experience a similar sensation with his cast of attackers.
I could pick out any of Chelsea's current attackers – probably with the exception of Mason Mount – and either bring up my previous work or conversations I've had over "how to get the best out of X player".
All players need suitable environments and will thrive in certain positions over others, but as football at the highest level becomes more defined by tactical flexibility, you cannot afford to carry many questions in your squad.
A coach like Tuchel has proven throughout his career at Mainz, Borussia Dortmund, PSG and now Chelsea that he likes the freedom to alter the shape of his squad depending on the situation.
His recent alteration to a 4-1-4-1 shows us a glimpse of where the German is looking to take Chelsea in the coming months.
Sadly, Chelsea already have too many players that need a number of specific compensations for them to play their best football, rather than them elevating the system.
"This is a team sport and it's not about ten players serving one player. It is not Chelsea and it is not football.
"Every player is there to serve the team. This is the highest principle and won't change." was Tuchel's firm response when responding to a question about the team changing to get the best out of Romelu Lukaku.
You could extend this to Jorginho – brilliant for Tuchel but one who suffered when asked to defend in bigger spaces under previous coaches.
Timo Werner – needing to play in transition with a strike partner.
Hakim Ziyech – excelling more in a back-four system where he has more creative freedom.
And Lukaku, who has proven to be one of Europe's best frontmen but has looked better when fielded alongside a strike partner and in a faster-paced game.
Chelsea cannot afford to waste years trying to unlock players that fail to produce the consistent performances required. Especially when Tuchel is up against two clubs who are run so efficiently in not tolerating many Pogba-like situations.
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