Stupid, You Can Call Me That...But You Have No Idea
Minor musical triumph for the theoretically retarded (me):
Scales.
On guitar. Real scales, across the neck, not just up and down one string (duh).
It seems you're supposed to envision a "box," but I could never figure out what to do with the dots in the diagrams. It turns out you have to learn the notes (and the intervals of that particular kind of scale), then you know exactly where to go (duh). Then you can put the box wherever you want and it still works. Ha!
I'm pleased, but still largely ignorant. It took me a book and bunches of time to figure it out.