Unsurprisingly, what we consider fundamental to effective self-defense relates directly to our objectives when teaching a course.
As we said on the main WSD page, three things are necessary for effective self-defense (unless you are lucky): knowledge, awareness, and appropriate behavior.
Items that are fundamental to a self-defense course should teach the above. Fundamentals should enable students to fulfill the objectives of the self-defense class---the upshot of which is that each student should have the tools necessary to keep themselves safe.
More importantly, those fundamentals should come with clear understanding (and practice!) of the self-defense mindset. The mindset is simple: you have value. You have value, and thus it is right that you should protect yourself. You have a right to make your own choices, to stand up for yourself. You should believe in yourself, and not be required to submit to someone else's force.
Value yourself, maintain awareness, make appropriate choices, and keep yourself safe.