I've been teaching guitar for 25 years, but my first student was me.
At 17, I was playing several instruments, drums, organ, guitar, saxophone and flute. At this time, if someone wanted to learn music, one had to work classical music, or sometimes jazz. But teachers were rare, and I wanted to learn pop music.
Of course, guitar was interesting me, but the problem with this instrument was that it could not hold notes for a long time, like winds or organ. It is when I heard for the first time Robert Fripp playing guitar solos on "21st Century Schizoid Man" and "The Sailors Tale" on the live album Earthbound by King Crimson, that I finally decided to choose guitar as my instrument, and R.F. as my teacher.
But Fripp was far from Nice, where I lived, and he was far from giving any guitar lessons. So I took on my own to create exercises to develop my skill. Some exercises were inefficient, some were unreasonable but with time, I understood that a good exercise must be either focusing on one spot of mechanical difficulty, or simulating a real play situation with a more or less complex overlap of techniques.