When I told my school music teacher I was learning guitar, he said, "You'd do better to learn a proper instrument, like the violin". Now, I wish I had.

When I started work, our company had a (very good, competition level) brass band, and the guy who ran it asked me to go to their practice night and take up a brass instrument, but I didn't have enough self-confidence to go. Wish I'd done that too.

And, according to one or two members here, I'm still a crap guitarist. :-)