The Fretboard

Diatonic theory is weighted towards 3rds (usually alternating major minor major minor major minor or minor major minor major minor major) so we don't get too many augmented or diminished chords. So it's great that the guitar is tuned in perfect fourths to make it easier to fret these chords... no wait it isn't...

The instruments tuned in 4ths (except for that major 3rd) and the chords are mostly built of stacked 3rds.. what does that mean? It means we can quickly construct any root inversion of a chord by planting the little finger on the root note, and planting the 3rd finger a fret or two higher on the next string and the second finger a fret or two higher on the next string and the first finger a fret or two higher on the next string.

Much is made of scale patterns living on the same 4-5 frets and that's great for learning 2 octave scale patterns, although it's good to play backwards to the root note when you hit either the highest or lowest notes in the scale... but diagonals - don't seem that interesting to people.