Sir Alex Ferguson says you don't win the title in December and he's dead right - but you can lose it.
United have to pick themselves up and go and win the next five games
Winning the Premiership is all about pressure: how you deal with it and how much you can apply on your opponents.
Unquestionably, the pressure is right on Manchester United after the defeat by West Ham on Sunday, which means their lead is now down to two points.
Ferguson's side didn't play particularly badly but they came up against a team who raised their game for a new manager and proved that their league position is completely false.
West Ham's performance only increases my sympathy for sacked manager Alan Pardew, who should have been given more time.
There is no way that team could ever have gone down but the penalties for failure are so great now that the new owner has come in, smelt relegation and opted for a change.
A bad afternoon for United was made worse by Chelsea's comeback to clinch victory at Everton.
You have to admire Jose Mourinho's side for their resilience. They just seem to thrive on adversity.
23 Dec Aston Villa (A)
26 Dec Wigan (H)
30 Dec Reading (H)
1 Jan Newcastle (A)
23 Dec Wigan (A)
26 Dec Reading (H)
30 Dec Fulham (H)
2 Jan Aston Villa (A)
They had problems with their goalkeeper and their centre-backs against Everton and yet they still came back and won with two unbelievable goals in the last few minutes.
It was the same in the draw against Arsenal: they just keep going until the final whistle.
Chelsea may not be playing that well and they may have another gear, but sometimes it isn't easy to find it in the middle of the season.
However, the most important thing is to keep applying pressure on the opposition and after Chelsea endured a little bit of pressure when United opened up an eight-point lead, they have piled it back on Ferguson's side.
Looking ahead, Chelsea and United have similar festive programmes and when you look at each fixture, you expect both to win all four games, but it's not that easy when the games are coming thick and fast.
What is important for United is how they respond to losing to West Ham.
It is a fact of life that you can't win every match and sometimes you play half-decent away from home and you don't win.
What United have to do is pick themselves up, dust themselves down and go and win the next five games and, over the years, they have been very good at doing that.
Winning a game at all would be a boost to both Charlton and Watford, who find themselves looking a little isolated at the bottom after West Ham's win.
But there is a massive difference between the two teams.
23 Dec Middlesbrough (A)
27 Dec Fulham (H)
30 Dec Aston Villa (H)
2 Jan Arsenal (A)
23 Dec Liverpool (A)
26 Dec Arsenal (H)
30 Dec Wigan (H)
1 Jan Fulham (A)
Watford were a zillion times better than Charlton and they should have got something from the game at Newcastle.
You know that they will keep going for their manager and their supporters - even though it might just be that they don't have enough quality to survive.
Charlton, meanwhile, were just abysmal against Liverpool.
With their line-up, they should be doing a lot better and I can only imagine it will be doom and gloom in training this week.
Just like United at the top, the only way Charlton can pick themselves up is by winning matches - but after that awful display on Saturday, it will not be so easy.