The Newcastle defeat was a sickener, but it also served as a timely reminder.
Watching Manchester United pick up a point, in the circumstances, would have been tough to take, given how tight the battle for Champions League qualification is.
Despite losing at St James' Park in the previous three seasons, United were facing a team in torrid home form and playing with 10 men for the entirety of the second half.
Yet, rather than building on Casemiro's late first-half equaliser, the Red Devils flopped to another loss on Tyneside. As I say, sickening, but perhaps an important lesson.
Because don't get me wrong, Michael Carrick is doing a fantastic job. He has lifted the team away from the prospect of another woeful Premier League campaign, in turn, handing fans hope of an unlikely Champions League return.
That said, talk of Carrick getting the United job permanently is wildly premature. As every game of his 10-match unbeaten start as interim boss passed, that talk only got louder.
But there has always been a crucial element that I won't have been alone in anticipating. We are yet to see how Carrick's United respond to defeat.
Now, after William Osula's 90th-minute sucker-punch, we're about to. And the occasion couldn't get much bigger in the current setting.
A match against Aston Villa at Old Trafford awaits on Sunday, at the end of an 11-day build-up.
Unai Emery's side are level with United on 51 points and, therefore, a direct rival for a top-five finish, in case you needed reminding.
Any judgement on Carrick must wait until the end of the season, because momentum in football is a phenomenon and is capable of changing the picture entirely.
If United can instantly get back on track and conquer a direct rival – who are currently in free-fall as it is – it will be full steam ahead.
If not… the wheels could very easily fall off, with the only match in the following month a tricky test at Bournemouth.
It's no understatement to suggest the Villa result could shape United's season, and future.
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