I learned not to take myself seriously. If you screw up, screw up BIG, and enjoy your own imperfections.
Conversely, I learned that accepting others screw ups (no matter *how* much better you think you are than they) makes for a much nicer world (musical and otherwise).
I learned that I have a *looooooong* way to go, and that there is *no* such thing as "getting there". That it is all about the journey.
I learned that, if it is not fun, don't do it.
I learned that, even when it stops being fun, you'll still want it.
I learned that there is no one way to do a thing, but there are some wrong ways.
I learned that humility before the fact makes it a lot easier after the fact to deal with messing up.
I learned that "professionalism", "good musician", and "nice person" are not synonymous, and if you *ever* meet up with someone who has all the above, you better darned well pay attention.