After reading once and making a note, you read the book again. You use doubled time and read in detail. In this phase, the goal is to eliminate things you do not understand. You recorded them in the first read through one by one. If you find a new unknown thing, you record it. Repeat until you understand. You do not go ahead if you do not understand.

Akinori Takada classifies the reasons for "I do not understand" into four.

You need to resolve each "I do not understand" one by one. It is important to know what kind of "I do not understand" it is.

Footnote:

I received a question. Sometimes the problem is caused by an incorrect description of the book. Isn't it?

Yes, sometimes the description in a book is wrong. If you spend 40 hours to understand the wrong book, it is a big loss. To reduce the probability, we need to choose the book for slow reading carefully. I introduced shelf-viewing in (4.4.2.1) Read the shelf and other methods in (1.2.5) How to choose better paper book?.