Today's generation is continuously taught that everyone is unique and different and generalizing is wrong and inaccurate and for those who don't like to think; every teacher is different, and every teacher teaches differently. Thus, I have no idea how I keep running into these same idiosyncrasies.
I introduce to you, The Pet Peeve. Anyone who has ever been in an English class will recognize it. The most common "Pet Peeve" is the "You" word.
The teacher walks in front of the class and announces this to be the biggest mistake. "Do not use the word 'You' in a formal essay." He then proceeds to fixate on that for the rest of the semester. It has been so ingrained into my generation's head of the evil the word "You," and, quite frankly, we couldn't care less anymore. After entering into college, the student has either been emotionally programed to avoid the word like a police car, or become so desensitized or spiteful that it becomes every other word in the essay.
The Pet Peeve can be anything. I had a screenwriting teacher who was obsessed with only writing what can be shown. I had an art teacher who wouldn't allow anything to be one color. Passive sentences, show don't tell, etc. It's usually accurate, but the teacher fixates on it. He gives very little advice in other areas of the work. It is also not usually not the most important thing needing to be fixed. It's doubtful that a bad essay that has its "You's" removed would thusly become a good essay.
The problem: The student already knows the rule. He has either just slipped up or chosen not to agree to it. When the teacher comes up and repeats the rule, the student then thinks one of two things: "My essay is perfect, and you can't stand that," or "My essay is crap and you don't know how to fix it."
The Pet Peeve soon becomes a cliche. It's taken completely out of context and impossible to use as a useful tool. It's like stating "Red is bad" and then sending someone into an art gallery. He no longer appreciates the art, he only can see, pardon the expression, red. And even if he chooses to just ignore the idea (which doesn't benefit him) he still can not go by a portrait without looking to the red first.
Everyone has their Pet Peeve. My parents watch a movie and they can't stand the quick camera angles. I watch an action flick and I cringe at the High-Strung, Voice of Morality love interest. It's not something easily ignored, nor something to be ignored, it just, also, can completely conceal the real issues.