I attempted to get into guitar years ago and quickly burned out. I never properly learned theory and was never able to play what I heard (either in my head, or by listening to music). Playing downloaded tab music was not enough to hold my interest.
I want to take another shot. After reflecting on why it didn't work out the first time, I came up with a theory. All of the theory references I've used in the past taught by bombarding the reader with ideas without any deep explanation. The analogy would a physics professor presenting his students with heaps of equations with no derivations, and expecting the students to take his word for it. For me this does not lead to true learning, and I quickly lose interest.
So to my question: is there a good music theory book / site / youtube video(s) (preferably with the guitar in mind, but not required) that presents the theory while simultaneously providing explanations? Something that does not depend solely on memorization, but rather, on understanding?
An simple example would be octaves: why do we use them? why are there 8 notes? why do notes 1 octave apart sound "the same" (I know there is some deeper physics here, but even a simple nod towards integer multiples of frequency) etc. Another example would be scales - rather than just presenting scale after scale, a deeper explanation as to how these are derived and why they are they way they are would be very beneficial to me.
I'm also open to criticism of my approach in general.