Watch out for Lionel Messi's final goal. You'll see it in a high-pressure match where he's already scored once or twice; when it arrives, you'll notice that this goal is far more spectacular than the ones that came before it.
Witness, for example, the first leg of this season's Barcelona's UEFA Champions League semifinal against Liverpool, in which Messi found the net twice last week. His first strike was a routine affair, following up to tap in a Luis Suarez shot that had fallen kindly to him after pinging off the crossbar. His second, a free-kick from a distance most might expect to be fairly safe, set social media alight.
Each new video of this goal, shot from a different angle revealed another level of Messi's beguiling brilliance. Watching it, you felt that Alisson, Liverpool's unfortunate goalkeeper, couldn't have stopped it even if his team had punctured the ball and turned off the stadium lights.
Many of us wonder at just how good Messi is. Yet we marvel even more at just how much better he seems to be getting, often in the course of the same match despite being on the "wrong" side of 30. The effect is similar to that of seeing an elite tennis player, having gone up two sets in a Grand Slam, become truly relaxed and start to make extravagant groundstrokes.
It is often said that to be at their best, footballers should play with freedom, but it's rarely stressed just how difficult that actually is. To have the calmness amid the fury to place a strike or pass as if you were still back in the schoolyard: that's the preserve of precious few players, and it all comes down to a supreme sense of occasion.
Andy Barton, a performance consultant who works with several leading UK athletes, has spoken of how Wayne Rooney treats the atmosphere in a soccer stadium; to him, it's a stage where the audience have gathered with the excitement of seeing him in his element. For Rooney, said Barton, there is no pressure, at least not at the level you might expect; instead, when he looks up at the stands, he is energized and exhilarated that so many people have come to witness him at work.
It's possible that for all of his reserved nature off the field, Messi has a similar approach. Basically, he's an absolute diva in the best possible sense of the word.
Look at the regularity with which he first adds his name to the scoresheet and then escalates. Against Real Madrid in the 2011 UEFA Champions League semifinal, he first scored from close range and then charged at the heart of the Madrid defence, a surge as thrilling as it was unassisted, before rolling the ball slowly beyond Iker Casillas. In 2015, at the same stage, he thrashed home a low drive from outside the area -- a fine effort, yes, but utterly ordinary by his standards -- before making Jerome Boateng feel as though an ice rink had appeared beneath him and floating a chip over Manuel Neuer.
When Messi elevates his level of play, it's interesting to watch the reaction of his opponents. Boateng was so irritated by the mockery that he received that he took to social media to defend himself. Pep Guardiola and Jurgen Klopp merely shrugged when exposed to similar acts of magic. Their reactions were equally vulnerable, equally human. What, after all, can you do? There are entire dressing rooms of footballers who would have claimed some of the game's greatest prizes but for one simple phrase: "Messi happened."
Messi happened against Madrid, against Bayern and, last week, against Liverpool; to have a chance of reaching the final, down 3-0 from the first leg, Klopp's men must somehow ensure that this consummate diva does not feel like adding a signature flourish.