We have all read terrible textbooks. What makes a textbook hard to read. There are several reasons. One is on the teacher’s side. The other is on the student’s side.

To understand why there are so many terrible textbooks, we need to put ourself into the shoe of the teachers.

As a teacher, when we write textbook, you don’t want to write something that is not “correct” or can be easily interpretted incorrectly. So you try to explain a concept you constantly go back to make it more formal or adding more details to it. In this way, the textbook becomes comprehensive but also not “human-readable”.

As a result, directly repeating the lecture would make a “wrong” textbook, so people usually chose the easy way to try to fix from that to make it correct. To write a good, readable textbook, one has to choose the hard way. One need to resist attempt to find an immediate fix to correctness issue but also think about how you would adjust the lecture material is told instead of simplying modifying the existing lecturing material.