After studying even more games, it dawns to me that perhaps more learning doesn't mean understanding. When people reached a certain level of studying materials, they would more try to find out and memorise a pattern, rather than being ready to decipher a completely new problem all over again one after one. It is not understanding, but reciting. Unfortunately, that is the majority of players, and that's why they keep on getting surprised when beaten up by younger players. They are not playing chess, they look at their past record, feels good, and say that comparing the experiences there is no way they can lose.