It's become fashionable to say you've learned something from a football match these days.
It's not enough to know the score, who scored and how it all affects the league table. No. There has to be something more.
Open a newspaper or check the internet after a game, and there will be someone, somewhere, who has learned something. Sometimes it's five things. Sometimes six. But there is always a lesson.
Even without the Scot in charge, United were stunted and lacklustre.
Their defending for Seb Larsson's goal in the first half was poor. And going forward, they lacked the invention to break down Sunderland's defence.
When West Brom, Everton, Newcastle, Swansea, Tottenham, Liverpool and Manchester City won at Old Trafford, they were termed "David Moyes defeats". But he's thousands of miles away in the United States and it's still happening.
You can only conclude that the problems that have dogged this season aren't all of his making.
And it follows that when, as expected, Louis van Gaal is appointed this week, it will not solve all United's problems.
It will take a successful and well-managed summer transfer window to get the club back into the Champions League.
The defeat to Sunderland means Tottenham need just a point from their final game of the season against Aston Villa to deny United European football next season.
Privately, the board have insisted that won't stop them chasing the world's best players. They can only hope those players don't mind skipping the Champions League for a year.
It will give them confidence, then, to see German newspaper Bild, reported by Metro, speculate that Thomas Muller wants to join former Bayern manager Van Gaal at Old Trafford.
He may not be the centre-half or central midfielder United desperately need. But he is one of the best players in Europe, playing for one of the best teams in Europe.
Providing Bild are right, it can only be good news that a player of his calibre wants to sign for United and Van Gaal.
If Muller is keen, then so might the rest.
United need more players who can boast Muller's talent and experience. It is vital if this season is going to be remembered as just a blip rather than the start of serious decline.
The defeat to Sunderland taught us that much at least.