What is the best meaning of the under line phrase hit a wall in the paragraph​

The effect of poor teaching can have a damaging effect on a student's understanding of and appreciation for a particular field of study. in my case, at university i was turned off trigonometry by a nervous prof who would back up and knock the chair off the teacher's platform and go through the lesson much too fast to be able to grasp the concepts so i failed his course. theand n when i bought an excellent book which explained trigonometry in a very sympathetic manner i was able to understand it and wrote a supp on it and got a b with my own effort.