I decided that I would learn more than the bare minimum of music theory to write this book. Partly, I want to demystify it for myself: a lot of it seems complicated, but a lot it is not all that difficult once you've learned a few basics. It builds on itself cumulatively, and things I barely knew a few months ago are now ingrained in me.
If I learn more than I need to know, then the book will have more depth, even if I don't actively use even a tenth of it. I refuse to be a dilettante.