True story...
A bunch of buddies of mine had a band. Kind of a hardcore type outfit but a little more technical than the average hardcore act. So their bass player left for whatever reason and they wanted to hire a good friend of ours. Really good guy (which is why the band wanted him) but he had never played an instrument in his life. Knowing that I had gotten other complete newbies band ready for my own projects and had actually been teaching their guitar player casually for years they asked if I could help. The guy in question was really skeptical and couldn't really understand why they wanted someone who had never played a note in his life but he was willing to give it a shot. I told him that I'd meet him at their rehearsal space before they had practice every week to show him some stuff but warned that we would have to do this for at least a few months.
So the first night I just wanted to show him how to hold the bass, pluck the strings and some basic communication stuff so when someone told him to play a specific note he could (basically "These are the frets, each fret has a number. These are the strings. They each have a name. Here are the names. If some one asks you to play at the X fret on the Y string just count up from the nut or the dots".
Second night I showed him some exercises. Just some chromatic stuff and a couple simple patterns.
Dude didn't need another lesson after that. I encouraged him to let me teach him some theory but we were both busy and he had already learned all their songs. He had his first gig with them the following month and was one of the most rock solid, if not simplistic, bass players in the immediate scene. Played right in time with the drummer and had MEAN power.
Astounding.