It is worth asking why these results keep happening, why a competition that once was marked by its caution and its caginess has become so chaotic. Allegri was not, particularly, in the mood to do so Tuesday — “These things have always happened,” he said — though he did suggest that the quality of the teams, as well as the sense of a second chance even after a first-leg defeat, might feed into it. And perhaps all of those precedents, too, have persuaded players that there is no such thing as a lost cause.
But that is only telling one side, allowing the victors to write history. What explains the gulf in performances over the course of two games for the losing teams: for Atlético and Real Madrid and, invariably, P.S.G.? Is it complacency, the converse of the avenging energies of the defeated? Is it the exposure of some fatal flaw? Is it an inherent respect for the epic?
Or is it — as Luka Milivojevic, a Serb midfielder for Crystal Palace, put it earlier this season — something to do with the nature of the challenge? A team like Lyon, he explained, is able to carry a game to Manchester City in the Champions League in a way that could not happen domestically because it is used to having the initiative; its default mode is to have the ball.
That is true of almost all of the teams in Europe’s elite competition. They are unaccustomed — even Atlético, whose reputation for doughty defending is rooted in its performances against Real, Barcelona and in the Champions League — to ceding control.
That tends to make games much more open, much more exciting, much more chaotic; and when an opponent can wrest the momentum from them, it makes them much more vulnerable. They are placed in a situation they do not have a great deal of experience in handling. They are powerless to resist. Perhaps that is what has created this version of the Champions League, where anything can happen, where improbable is not enough and impossible might not be, too, where it is worth giving something, no matter how fantastical, a go.