Two's company, three's a crowd—or so the saying goes.
In terms of central defenders, it's a proverb that proves particularly apt with a four-man back line, with one player always missing out and left to watch his team from the sidelines.
At Stamford Bridge this season, that man has often been David Luiz.
For one reason or another, the Brazilian hasn't played as much as he would necessarily like under Jose Mourinho, who has preferred the John Terry-Gary Cahill partnership at the back. It's a move that has paid off, though, with Chelsea yet to lose a game when their England pairing has been present.
Whether it's an innate cultural understanding or simply that their attributes complement the other, Terry and Cahill have made the type of start that to the campaign that will have a major influence over the next nine months or so if Chelsea are to reclaim the Premier League title.
Jose Mourinho has said it himself these past few weeks; however, that he remains at odds as to who will be making the Blues' starting lineup.
"Of course, I don’t know [what my best team is]. But the players have to give me the answers," he was quoted as saying by the Evening Standard.
With this in mind, Bleacher Report analyzes the prospects and talents of the three central defenders the Portuguese has at his disposal.
He's been Chelsea captain for the best part of 10 years and his leadership qualities alone ensure John Terry stands out from the rest of Chelsea's defenders.
Now 32, Terry may no longer have youth on his side, although he has lost none of what has made him one of the finest defenders of his generation.
His positional sense remains a key attribute, while he is a commanding presence in the air and leads by example, often pulling his team back from the brink on his sheer will to win alone.
There has long been a criticism as to his apparent lack of pace, but he more than makes up for it in other areas. He reads his opponent well, and with a physical edge, there aren't many strikers who can say they have got the better of Terry over the years.
With Chelsea's revised style and ethos these past few seasons, Terry's lack of dynamism compared to the alternatives at Jose Mourinho's disposal will be of a concern as this Chelsea team develops. Yet, for now, there isn't any other player in Terry's position who can claim to be his superior.
2013-13 Premier League stats
After a quiet 18 months in West London, Gary Cahill has come of age this season.
The Englishman has long been admired for his talents, but there has been an impression that he needed to step up another level to be considered in the same class as John Terry, David Luiz and his teammates in the England team.
This year has seen him do that, with Cahill one of the standout performers for club and country.
It's an encouraging development, too, given that Terry's age means his time at the top is rapidly reducing with every passing season.
The 27-year-old may not be captain material, although he is beginning to show he has the ability to become a key part of this new-look Chelsea.
He is quick off the mark and growing stronger physically. As he enters the prime years of his career, Chelsea's £7 million investment in January 2012 is looking a very shrewd move.
Cahill does have a tendency to leave himself exposed at times, but then with the caliber of opposition he often faces, he's not the only centre-back who will criticised for that over the course of a season.
2013-14 Premier League stats
Once described as a being like a "PlayStation player" by Sky Sports pundit Gary Neville (via Daily Mail), there's no doubting David Luiz has become more disciplined at the heart of defence.
In fact, he was one of Chelsea's best players last term, stepping up to the plate when John Terry was sidelined for the best part of two months with a knee injury and showing tremendous maturity.
Such was Luiz's form in 2012-13, interim manager Rafa Benitez found it difficult to reintroduce Terry to the fray, with the Brazilian and Gary Cahill becoming his preferred defensive partnership.
When Terry did play under Benitez, however, Luiz was moved a little further forward into a defensive midfield role at times and flourished.
Typical of a player heralding from South America, the 26-year-old has a considerable bag of tricks in his repertoire. The only problem being they are not always suitable for a player who does much of his work in the defensive third.
There's a growing feeling among supporters and pundits alike that Luiz should be given more of a midfield role by Jose Mourinho and it's a view that stands to reason.
Playing so deep is restrictive for Luiz. He knows the ability he possesses and while it's a considerable attribute, it's also proven his downfall in the past.
Against Everton at Goodison Park this season, Luiz was the man at fault for Steven Naismith's goal that eventually proved decisive as the game ended in a 1-0 defeat for the Blues.
Caught out of position due to his desire to be drawn into action, he left his partner Terry exposed and Everton capitalized.
He was heavily criticized, yet whenever Chelsea were on the front foot in that fixture, it was often their Brazilian centre-back helping push them forward.
Moving him further up the field as Benitez did at times last term appears a wiser move with each game for Luiz. Given the form of his teammates—and defensive rivals in the best possible sense—Terry and Cahill, it also seems a move Mourinho may find difficult to overlook.
2013-14 Premier League stats