That doesn't mean that the more you learn, the more flexible your brain will be. The more you do problems, the more you can integrate what you have learned and feel comfortable when you do problems. I don't know if you feel this way. Can't do the problem, or it takes a long time to work it out. As a result, I found it was as simple as that after reading the answer. This is that you just don't have the habit, and you just can't do it if you know it, so you need to do it.