have a one-track mind
Fig. to think entirely or almost entirely about one subject. Adolescent boys often have one-track minds. All they're interested in is the opposite sex. Bob has a one-track mind. He can only talk about football.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs
He has a one-track mind. All he ever talks about is trains and railroads. YourDictionary
Most folks have a one-track mind, and I even want to say, a "single-minded obsession" about "note-taking".
From the standpoint of productivity, "note taking" is just a very small part of the information gathering equation.
Most folks don't know there is another important part, and that's, "note-making." Quora
have blinders on/be wearing blinders
Blinders are coverings placed over a horse's eyes which prevent the horse from seeing anything that isn't straight ahead. When wearing blinders, the horse can't see anything to the sides. This helps prevent a horse from being scared by things it can't see.
The idea is that if you're wearing blinders, you have a very narrow view of things, and you aren't aware of everything that's happening around you. If I tell you to take your blinders off, I'm really telling you to look at everything around you and make an informed decision based on all the information available, instead of just making decisions based upon what you know by only looking at a small part of the problem.
Not to be able to see the big picture
the big picture also the whole picture
the most important facts about a situation and the effects that it has on other things Melissa's opinions don't take the big picture into account.
Usage notes: often used after look at: When you look at the big picture, a slight increase in unemployment is not significant.
Cambridge Dictionary of American Idioms
be sitting too close to the screen to [take in/see/get/grasp] the whole picture
be looking through the wrong end of the telescope