Chelsea's struggles to adapt to Maurizio Sarri's methods this season have stemmed from a lack of a solid defensive base, and are a sign that the Blues must move on from David Luiz.
After flying out of the blocks at the same pace as Manchester City and Liverpool, the Blues have since faded away from the Premier League's title-chasing duo. A lack of consistency in goalscoring has partly been at fault, but their problems ultimately begin at the back.
While Liverpool and City have only conceded 20 and 22 league goals respectively this term, Chelsea have conceded 39. That remains the fourth best defensive record in the division, and reflects their position in the league table, but also explains why they are not in title contention.
The attacking brilliance of the top two could arguably justify a lesser defensive record, but both Pep Guardiola and Jurgen Klopp's sides have found an excellent balance which maintains consistency at both ends of the pitch - and that has stood them clearly apart from the rest.
Meanwhile, while City and Liverpool have scored 90 and 84 Premier League goals respectively this term, Chelsea have scored just 60 - only the sixth best in the division.
Therefore, Chelsea's attacking exploits hardly compensate for a defensive record which fails to keep pace with the best in the league.
Just as there have been moments where Eden Hazard has inspired Chelsea to attacking displays in which the Blues have appeared unplayable, and Jorginho has dropped the odd midfield masterclass, Sarri's side have on occasion defended with great resolve.
December's 2-0 victory over reigning champions City was a clear example of the Blues' ability to stifle even the finest attacking opposition, as did a 0-0 draw with Guardiola's side in the Carabao Cup final.
Derby's Player of the Year! — Chelsea FC (@ChelseaFC) May 4, 2019
What a season for @FikayoTomori_!
However, as with in other areas of the pitch, that clear showing of defensive quality has not been developed into maintained consistency at the back.
Sarri's style of play is clearly one which demands flair in attack, control in midfield and organised resolve in defence. Not one of those three have been exercised regularly this season, and for all three to succeed, it is the latter which must first be successfully implemented for the others to follow suit.
Whether it is Arsenal's Invincibles, Manchester United's successes with a Ferdinand-Vidic defensive wall during Sir Alex Ferguson's later years or even Chelsea's revolutionary triumphs during Jose Mourinho's first tenure, recent title successes have always been built on solid defences.
In John Terry, Chelsea groomed their own defensive rock, uncompromising leader and emblematic club figurehead, whilst Mourinho also brought the seasoned Ricardo Carvalho with him from Porto to stage the Blues' tide-turning title victory in 2004/05.
Sarri's appointment at Stamford Bridge last term appeared designed to have a similar impact in west London to that of the iconic Portuguese tactician.
The Italian's meticulous demands and bold style of play at Napoli had become similarly notorious to the ground-breaking coaching methods of Mourinho during the earlier years of his career.
The boss says Andreas Christensen is ready to play and he hopes he will be very mentally and physically fresh. 'I am really very confident in Andreas. He has played some very important matches very well.' #FRACHE— Chelsea FC (@ChelseaFC) May 1, 2019
Where predecessor Antonio Conte had favoured a trio of central defenders during his tenure in west London which featured Cesar Azpilicueta, Andreas Christensen and Antonio Rudiger as a back three with accompanying wing backs, Sarri opted to start over.
His favoured back four was implemented but, crucially, Sarri failed to add defensive reinforcements, with the seasoned outcast David Luiz restored to the side in place of the promising but unpolished Christensen.
The back four is clearly a preferred tool in Sarri's approach to more progressive football than was previously seen at Chelsea, but the composition of that defensive quartet has since lacked the required discipline and resolve for the Italian's approach to succeed.
By contrast to Mourinho's title success during his first season in charge at the club, Chelsea's current defence lacks any such mirroring of Sarri's image to that which his Portuguese counterpart implemented with great success.
David Luiz, in particular, was re-signed by the club in 2016 as something of a mercenary recruit in Antonio Conte's last-ditch bid to strengthen his defence after missing out on other targets.
The Brazilian ultimately fell out of favour under Chelsea's previous head coach, and his restoration to the side this season appeared at first as a sign of Sarri putting his stamp on the team.
Ultimately, it has been proved that Luiz is not a Sarri player in the sense that Kalidou Koulibaly was at Napoli, nor is he a parallel in his ability to lead the Blues' backline in the 'John Terry' position at the heart of a revised back four.
At 32, the Brazilian is no longer a 'blank canvas' of a player who is open to re-moulding, nor does his cavalier approach to defending provide the key to a solid defensive base which is yet to be put in place under Sarri.
Andreas Christensen started the season in a similar position to that which Terry was in during Mourinho's maiden campaign. A young defender who has progressed through Chelsea's youth system, the Danish international has the potential to develop into a real leader in defence.
Luiz is a flamboyant journeyman, but Christensen is full of potential and has the ability to grow into the 'John Terry' mould as the Blues' rock at the back for many years to come, with greater potential, solidity and longevity than Luiz.
Not only that, the 23-year-old has masses of potential which is yet to be fully unlocked, and Sarri's ability to yield the best from the Danish prospect could help the Italian put a more telling stamp on his side.
The recycling of older stars has proven to be an ill-advised move on Sarri's part this season, but with the likes of Christensen and rising star Ethan Ampadu on the books at Chelsea, the Italian has a glaring opportunity to oversee the development of a highly promising crop of young stars.
With Sarri having struggled to fully implement his coaching ideals and yield title-worthy consistency from his side this season, it is time for Chelsea to move on from unsuccessful formulas and focus on developing their stars of the future.