No, you are not stupid.
The Ten Chi Jin is a manual for instructors in the Bujinkan. If you do not teach, don't worry about not knowing what the heck it is. It basically outlines all the stuff an instructor should know and teach. It is not a limit, but if you do not know something in it, you have a hole in your knowledge. If you don't know, say, a naginata kata that does not appear in the Ten Chi Jin, it is not considered a big thing. But the stuff in the Ten Chi Jin is the bare minimum you should have in what you teach.