I think it went something like this:
Before leaving school I discovered The Shadows, and thought that this electric guitar music sounded awesome, much better than what my peers at school were listening to (this was the 80s) and more exciting than the classical music pushed via school music lessons. Listening only is never enough, so I saved money from holiday jobs to get a cheap electric guitar (Hohner flying V).
But, good as it was, there was something lacking, so I tried listening to blues, rock & roll, funk etc. to see if I could find what I was after. Eventually, I discovered that it was jazz I wanted to listen to and play. As an undergraduate, I learned how to do big band style rhythm guitar and joined the university band.
When in this band, I realised that bass sounded rather cool. There wasn't any opportunity to play bass at the time, but when I graduated I bought an unlined fretless electric and switched over (here's an example from a year later).