"Never his mind on where he was, what he was doing." That was Yoda's complaint about Darth Vader, and the same can be said about a class of student pilots that I like to call over-analyzers.
I've seen it happen at all levels, from the private pilot-to-be all the way up to the new-hire airline trainee. The student knocks it out of the park in ground school, but things go sour once they get to the flying.
The over-analyzer usually does quite well when conditions are perfect. They fly the textbook traffic pattern, make a textbook steep turn and generally fly by the book. But when things are beyond the bounds of what they've studied, they will often freeze up, and it's all because their head is not in the game -- it's back in the classroom!
I think it has a lot to do with the overwhelming level of information available on flying any given maneuver. The textbooks break the maneuver into multiple steps, then discuss common mistakes, how to correct those mistakes, and then go on to list practical test tolerances. All of this is good information, but in the course of flying the maneuver, it's just not all that relevant.
For the student, I suggest focusing on the big picture. Don't get too wrapped up in all the common mistakes and maneuver standards in the textbook. Instead, focus on how to fly the maneuver and visualize what it's supposed to look like. If it isn't perfect, just fly the plane to where it's supposed to be and carry on.
Your flying isn’t always going to be pretty, mine certainly isn’t. But as long as you keep your mind on flying the airplane, you'll be on your way to being a great pilot.