That's how easy a lead can evaporate, that's how exacting a title race is, and that's how difficult a suddenly leaden Liverpool are now finding it.
This - as West Ham United made clear - is where it gets real. That can be seen in Liverpool's record.
Just five days ago, they hadn't slipped up once to any sides outside the top six, and this was seen as the primary reason they would use a seven-point lead as the platform for the grandest of victories.
That lead is now just three points, because Liverpool have now slipped up to such sides in successive games, with two 1-1 draws.
It serves as both consolation and warning, though, that this could have been a lot worse.
A hugely assertive West Ham deserved much more than a point, and not just because Liverpool's opening goal should have been called offside before it even got that far.
It was because they were so much the better side, creating so many superior chances. Manuel Pellegrii also out-thought Jurgen Klopp, but of greater concern for the German in the long-term should be how depleted and lacking in sharpness his injury-afflicted side looked.
They didn't drive anything home here and have now left open the possibility that they are behind Manchester City by the time they kick off their next match.
It already feels like the tone of this title race has changed, though.
If there was once a fear that the top two were just too strong for everyone and would win a critical mass of matches, things have taken a curious turn, where certain advantages have started to work against them. Namely, the biggest advantage of all: going ahead.
This was the fourth match in a row where one of the top two went in front early on only to make life difficult for themselves.
Liverpool also here had the advantage of the linesman's flag staying down when it really shouldn't. James Milner was obviously offside when receiving the ball in the 23rd minute, but waved through for Sadio Mane to then turn in his cross all too easily.
The moment was all the more of a bonus for Liverpool because of how nervy they'd looked up to that point, but another twist was that going ahead didn't settle them. It only made them worse, and only emboldened West Ham.
Not that the home side's performance was just down to force, or the extra finesse of Felipe Anderson. They were tactically outwitting Liverpool, especially on free-kicks.
It was impossible not to conclude that Pellegrini and his staff had spotted a clear vulnerability within Klopp's side down the flanks at set-pieces, so often did they go for it and get joy from it. This should be galling for the German.
It was where West Ham got their goal from, Anderson taking a short free-kick to slip in Michail Antonio to finish.
What was so remarkable was not just that Liverpool themselves didn't seem to realise this, or at least address it, but that West Ham were still getting through in this way no matter whether they played the ball high or low, long or short or left or right.
It should really have brought a second goal, only for Declan Rice to head over from one clipped Anderson ball.
Liverpool just looked so lacking in substance for long stretches of the game, and that was surely linked to the lack of substance to the squad.
It still isn't that deep, and there was a huge difference between the quality of their bench and the quality of Manchester City's against Arsenal.
That was of course a consequence of injuries to Dejan Lovren, Trent Alexander-Arnold, Jordan Henderson, Gini Wijnaldum and Alex Oxlade-Chamberlain - but that is also the point.
It so sufficiently weakens them, and also highlights the fact that their outfield summer signings - partly signed specifically for this issue - have not yet fully fired.
Fabinho has been adequate, even if there remains the question of why Klopp doesn't trust him at right-back when he plays there for Brazil and there are other injuries, but how would you describe Naby Keita?
He was supposed to be the force who lifted their midfield to another level.
He was instead all too easily levelled here, not least for Antonio's goal. Rice looked a lot more assured in that regard, and was almost the cause of another West Ham goal with a driving run, only for Hernandez and Anderson to get in a mix-up.
Xherdan Shaqiri has probably been the most productive of those signings, given how he just offers something different, and it was inevitable that Klopp eventually brought him on for Adam Lallana.
There was nothing different about their performance, though. Liverpool were still making hard work of this game, and have now made much harder work of this title race. (© Independent News Service)