Since its inception, winning the Champions League has proved to be a curse in disguise as none of the 12 different title holders have managed to retain the trophy in 20 attempts -- Marseille are excluded as they did not participate in the 1993-94 CL due to disqualification. Real Madrid face an almost impossible task in Europe this season -- the odds are heavily stacked against Ancelotti's men who are aiming to potentially rewrite history with a ground-breaking defense of their stupefying Décima conquest. Claiming the premier European football crown on ten separate occasions is incredible but securing it twice successively might be an even mightier feat. Eight clubs have done so in the past but all prior to the rebranding of the competition from the European Cup to the Champions League. Repeating victory in the competition in consecutive fashion has taken on a mythical status for post-1992 holders of the title.
The longest period of time without a back-to-back champion of the European Cup was approximately 10 years in its 37 year history. The CL, still without a back-to-back champion, is in its 23rd edition. Some could dismiss this peculiar trend as coincidence but there's more than luck or chance to the phenomena. Studies have shown that the current format of the tournament makes it extremely difficult for teams to win it twice in a row. Prior to 1992, the tournament was a pure knock-out competition and the group stage was only introduced with the CL. Groups serve as a buffer of sorts against non-persistent factors such as poor refereeing, form fluctuations, performance anomalies etc. They enable the quality of teams to reflect itself in tournament progression such that the stronger teams make it into the latter rounds with higher frequency.
The 'Closest Five To Successive CLs' graph shows the estimated amount of time between the last drawing/winning position - of title holders in the CL - and winning the competition in regulation time. The five sides shown were the closest to winning the CL twice in a row. The 'Rounds Eliminated' chart shows the stage/round the prior year CL winners were eliminated.
Another complication for defending champions was the rules change in 1999 giving 2nd and 3rd (later on) placed teams in highly ranked domestic leagues automatic CL qualification: this increased the pool of competitive teams in the tournament. Based on the minutes metric displayed in the chart above, the average minutes away from successive CLs was 122 pre-1999 and 237 (almost double) post-1999. The only post-1999 team to win the CL and make it to the final the subsequent season was Alex Ferguson's Manchester United -- spearheaded by Real Madrid's very own Cristiano Ronaldo. Dynasty sides, footballing powers of the highest order like Fabio Capello's AC Milan or Marcelo Lippi's Juventus, have come and gone without achieving the repeat. More recently, Barcelona's generational team of 6 years ago couldn't do it. Bayern Munich's juggernaut squad positioned to be the first side to do it were swept aside by Florentino Pérez's fabrication in April.
Today, the mission lies before the most expensive assembly of players in history and the landscape doesn't look any kinder than in years past. Jose Mourinho's Chelsea are in the coach's infamous "second year" and stand as the only undefeated (in all competitions) English side. His foe, Pep Guardiola, is taking Bayern Munich to seemingly new heights and has only suffered defeat once (in the Supercup) this season. Paris Saint Germain, also undefeated this season, have shown the capability to match their high ambitions. And these are just some of the heavyweights: the list of clubs that can cause damage on their day is endless. However, the Galacticos do not look fazed and are charging on at breath-taking pace. Real Madrid are coldly staring down its challengers. The weight of (im)probability pressing against their shoulders, Casillas and co are attempting the impossible.