This shows that you still don't understand the knowledge points of the topic investigation. Knowing how to do it temporarily and understanding it during the teacher's explanation can easily blind your heart and make you think you can, but in fact you don't understand why you should do it at all. Only when you know the reason of each step, can you think about why you didn't think of it, which is often a question of thinking mode. I have always maintained an inherent mode of thinking, and I have never understood why the answer is like this, so I will never make progress, or I am temporarily puzzled. If you want to get rid of this situation, first ask a few more why, not what the answer is, but what you should do, but understand this thought, turn this thought into your own inner self, or generate your own thought, so that you will never forget it. Second, summarize more. This is also a step to realize the change of concept.