There can be tactical errors and miscalculations, of course, but it's rare that things are as black and white as that. More often there are options, choices of emphasis and at times what is usually a strength can become a weakness. Even the very best players can, on occasion, become a liability.
Cristiano Ronaldo doesn't defend. He doesn't track his full-back. In most games, Real Madrid have enough possession that he doesn't need to. It could even be argued that he shouldn't: better to keep himself fresh and alert to produce the explosive bursts that have brought so many goals. But that unwillingness or inability presents coaches with a dilemma.
When winger or wide forward meets attacking full-back, there is no right or wrong way of dealing with it. When England beat Croatia 4-1 in a World Cup qualifier in Zagreb in 2008, for instance, Fabio Capello's solution to the threat of Croatia's attacking left side was to station Theo Walcott high up the pitch. Danijel Pranjic, the Croatia left-back, happily surged past him again and again, and again and again England broke and played the ball into the space behind the full-back. Walcott ended up with a hat-trick and by the end Pranjic was the picture of confusion, caught between the two stools of overlapping Ivan Rakitic and sitting back to defend.
But that doesn't mean that the best way to counter an attacking full-back is always to play the opposing winger high up the pitch. Manchester United deployed David Beckham high on the right away to Real Madrid in the Champions League in 2003 and he barely touched the ball, Roberto Carlos zooming past him again and again, helping Real to a 3-1 win. It helps, of course, that Walcott is so much quicker than Beckham was, that Roberto Carlos had the chance get back, but really it comes down to possession. In Zagreb, England had enough of the ball to take advantage of the space behind the full-back; in Madrid, United didn't. But then, one of the reasons Real Madrid dominated possession that night was precisely that Roberto Carlos gave them an extra man in midfield.
Ronaldo frequently poses this problem for coaches. In 2009, for instance, he had such a poor game tracking the left-back Aly Cissokho in a 2-2 draw against Porto at Old Trafford that Sir Alex Ferguson switched him to the centre for the return, using Wayne Rooney as the wide man. Ronaldo scored the only goal of the game. In the final against Chelsea that year, he was again deployed on the left. He scored the opening goal of the game, but from around the half-hour mark he was dominated by Michael Essien, whose untracked surge and shot just before half-time led to Frank Lampard's equaliser.
In the 2010 Champions League final, José Mourinho, then the coach of Internazionale, neutralised the link-up between Arjen Robben and Philipp Lahm, which is so vital to Bayern's play, by sitting Cristian Chivu deep at left-back and having Goran Pandev shuttle back from the left side of the 4-2-3-1. On Tuesday night, there was no similar option available to him. Lahm did his defensive job well – although he had less to do against Ronaldo than anybody could reasonably have expected – but was also arguably Bayern's most effective attacking player. Not only did he put in a number of dangerous crosses, but the threat of his overlaps also created doubt in the mind of the Real left-back Fábio Coentrão, who was left exposed and had an awful game.
That was, presumably, a risk Mourinho was aware of and accepted, and the number of long diagonal passes Xabi Alonso hit in behind the full-backs suggested a side trying to hit precisely the space England exploited in Zagreb – or at the very least to make Lahm and David Alaba aware of the danger of pushing too high up the pitch. Alaba, noticeably, got forward far less than Lahm. That may be because he is only 19 and, as yet, nothing like the player Lahm is; or it may be that Angel Di María is a very good tracker of a full-back – the one real surge forward the Austria international had came after Di María had moved into the middle and Ronaldo had switched to that flank.
Yet in the first quarter of an hour or so, until the incident in which Franck Ribéry found that a brush of his chest caused temporary paralysis of his legs (a moment that highlighted what we already knew: Ribéry is a serial feigner and Sergio Ramos is vulnerable when he's actually asked to defend), Real Madrid seemed not merely comfortable but in control.
The issue was possession. By leaving out Thomas Müller for Toni Kroos, Bayern's 4-2-3-1 was equipped with two relatively mobile midfield holding players plus, in Kroos, an attacking central midfielder more than capable of dropping back. By contrast, Mesut Ozil, playing in the centre of the trident for Real, tended to stay high, leaving Luiz Gustavo free – at least until Mourinho switched him and Di María midway through the first half; he changed them back at half-time. That meant Bayern were able to pressure Alonso, who looked exhausted, and Sami Khedira, which explains both the number of long balls they hit (not all of them calculated diagonals behind the full-back) and why Real Madrid's passing was so unusually sloppy. With Ozil, Ronaldo and Karim Benzema staying high, Bayern were able to pin Real Madrid back for long periods.
Bastian Schweinsteiger, just feeling his way back from injury, didn't have his best night and he too misplaced a number of passes, but he still had a positive impact in ensuring Bayern never became broken, as they had done when he wasn't on the field, against Borussia Dortmund last week. He was also caught in possession in the buildup to Real Madrid's equaliser. That was, admittedly, following a free-kick rather than from open play, but it still highlighted the danger of Bayern's midfield pushing up, leaving the back four unprotected – again we see the difficulty of assessing "good" and "bad": the tactic won Bayern the game but it cost them a goal.
In the end, it was basic defensive errors that cost Real Madrid. Ramos failed to deal with a corner, presenting Ribéry with the opener – and very nearly laid on a goal for Mario Gomez in similar fashion in the second half. Then Coentrão was beaten far too easily by Lahm for the second, while neither Alonso nor Ramos made any move to intercept the full-back's cross at the near post. This, of course, is the danger for sides used to dominating; when they do meet a resistant opponent, they've forgotten how to defend.
Had Coentrão or Ramos had better games, Real probably would have held on. But the issue of how Bayern were able to force those errors was tactical: they won the battle on the flanks, particularly their right, and they were able to do that because Schweinsteiger's advanced position (despite his errors) and Kroos's deep position gave them control in the middle. Mourinho claimed that Bayern's winner came "out of context" but that was true only in the sense it should have arrived earlier.