It has been a repeated failing of David Moyes' side this term that they have done well in cup competitions, only to fall away the following weekend.
The puzzle explains why United find themselves within a win of sealing a place in the Champions League knockout phase after only three matches, yet also staring up at the Premier League from an unaccustomed eighth position, eight points adrift of leaders Arsenal.
Once more, the Red Devils feel they are moving forwards following Wednesday night's 1-0 win over Real Sociedad.
But Carrick knows they cannot falter again when they face Stoke at Old Trafford on Saturday.
"The frustrating thing is we have had moments in certain games of when you think 'this is it, we're on the up'," said the England midfielder.
"Then in the next game for some reason it doesn't go how you would expect.
"That is the challenge we face.
"We have done well enough again, but then we have to on Saturday."
Nothing can be taken for granted though, largely because an explanation for United's troubles is so difficult to find.
"It is tough," said Carrick.
"You can look at the Southampton game last Saturday and say we really should have won.
"We were 1-0 up and had chances to score more. Then we concede from a corner.
"In that instance, you could say we can defend corners better but overall it is about fine margins and little details.
"In the past we have been good at getting on top of those things and seeing games out.
"I am sure we will do that in the games we have coming up."
Other than the heavy defeat by Manchester City last month and the subsequent shock home loss against West Brom, United have looked capable of winning matches.
However, as manager David Moyes pointed out immediately after the Sociedad encounter, too many scoring opportunities have been spurned.
Carrick does not view that as a major problem, certainly, he feels, missing chances is better than failing to create them.
"The attacking lads are looking dangerous, it is just not falling for them at certain times," said Carrick.
"You are more concerned when you are not creating chances and the lads aren't getting opportunities.
"With the quality we have I am sure they will soon start going in a lot more."
The absence of Robin van Persie with a combination of niggling injuries offered Shinji Kagawa a rare chance to shine.
It was particularly interesting to see how potent his combination with Wayne Rooney looked once he was switched to a central position for the latter stages.
"It was Shinji's best game in my time," said Moyes.
"We brought him in during pre-season and he hasn't really found his feet.
"This time I saw something from Shinji which I hadn't seen in other games. I was really pleased with that."
Kagawa's problem, as ever, will be if Van Persie is fit, he will be shunted back out to the left wing or dropped back onto the bench this weekend.
Moyes offered no further update on the fitness of central defensive pair Rio Ferdinand and Nemanja Vidic, who both sat out a second successive game.
Jonny Evans and Phil Jones have responded well though and a second clean sheet in eight games is another positive sign.
"There is still a way to go before we are really at our best but it was a decent performance and there are a lot of things we can work on," said Carrick.
- Sports & Recreation
- David Moyes
- Premier League
- Shinji Kagawa