First of all, let's make it clear that the so-called scum refers to the scum of science (mathematics, physics, chemistry) (English questions will be discussed later)

Let me talk about how scum is formed.

In the case that the previous knowledge is not fully mastered, learning a new section will lead to poor learning of the new section, that is, some knowledge cannot be mastered. Therefore, if the above behavior is repeated, the knowledge that has not been mastered will accumulate more and more, which will have a greater negative effect on the newly learned section, and the proportion of knowledge that cannot be mastered in the newly learned section will also increase.

Just like snowballing, the knowledge you don't have is just an unremarkable little snowball at first. With the increase of chapters, snowballs get bigger and bigger. When the snowball is big, the textbook can't be learned like a gobbledygook. And this process is the formation process of scum.

If you want to fight back, just contact me.