Thinking clearly under pressure: it's the thing that usually separates the great from the good, the ability to act normal in abnormal situations.
All through this week, pressure has been the word thrown at Liverpool. Can they handle it? Will it get to them? Pep Guardiola clearly feels it will. Before the collision dubbed Champions versus Challengers, he explained how hard it could prove for them to carry the weight of history.
Liverpool moved with the force and speed of a runaway train through December but it is true to say they had not faced an opponent like the one that was waiting for them at the Etihad Stadium; this, then, was going to be a revealing evening.
Liverpool looked anxious as they succumbed to their first league defeat of the season
What Jurgen Klopp would have wanted more than anything was a calm, assured start. Ease into the contest, quell the frenzy of the attacking 'thunderstorm' he anticipated and play with the poise of a team that can go and become champions.
But what he got was something altogether different. With only nine seconds gone, a ball that Sadio Mane would usually control with his eyes closed ended up skidding from his foot and out of play. Fair enough, you will say. That can happen to anyone at any time.
If Mane was anxious, however, he was not alone; with 70 seconds on the clock, Alisson Becker, the goalkeeper who rarely - if ever - gets flustered, sliced a clearance out of play in the fashion of weekend golfer clattering one out of bounds.
With their lead down to four points now comes the real test of nerve for Jurgen Klopp's team
The Brazilian did it again in the third minute, a straightforward pass to the centre circle not having enough weight on for James Milner to get there; Leroy Sane, a persistent threat, raced in and launched one of those rapid counterattacks when he looks like a motorcyclist weaving in and out of traffic.
Could Liverpool settle down? The answer was no. Minute four? It was Dejan Lovren's turn to miss his intended target. Minute
