IMO learning to draw is sort of like creating your own compression algorithm. There are many different ways to distill the huge amount of visual information into that which can be expressed through abstraction on a two-dimensional plane. The coolest part to me is that while some of these algorithms are lossy, others are...gainy? (what's the opposite of lossy...?) Depending on how you tune your simplification of the subject, the result can look MORE like the essence of the thing than the thing itself. The magic of caricature.
My girlfriend she's a painter and studied fine arts in a London art school.
First thing she told me is that everything is asymmetrical, if you're measuring distances, you're doing it completely wrong.
Second thin she told me is that details are completely useless - if not confusing - if you don't get the basic shapes right.
As you correctly point out it's like a compression algorithm, and like compression algorithms (as a computer scientist) I think implementing what's already working is easier than come up with your own new algorithm.
But, despite all the help I got, I'm - unfortunately for me - still a terrible draftsman.
