https://calteches.library.caltech.edu/2362/
"...I believe that every subject which is presented in the textbook should be presented in such a way that the purpose of the presentation is made evident.
The reason why the subject is there should be clear; the utility of the subject and its relevance to the world must be made clear to the pupil. ..."
続き><
’...I would take, as an example, the subject of sets. In almost all of the textbooks which discuss sets, the material about sets is never used - nor is any explanation given as to why the concept is of any particular interest or utility. The only thing that is said is that "the concept of sets is very familiar." ...'