From Guitar Player June 5 2005 interview with Steve Vai:
After all these years of performing and composing at such a high level, what still keeps you jazzed about being a guitarist?
It’s that the guitar is a virtually limitless tool of expression. Just the way you touch the note or pluck the string changes everything, and how a melody speaks on an instrument is really what determines the effect it will have on a listener. I love exploring the dynamics that are capable on the guitar. There’s not a single note I play that isn’t labored over until I’m in total control of the sound. The phrasing, the articulation, the dynamics, and everything else are carefully thought out and performed a million times. All of this is a tremendous challenge, but once I get to the next level of performance, the tough stuff becomes second nature, as well as becoming my new plateau—the place I’ll start from to develop my next period of discovery. And this is one of the beautiful aspects about evolving as a musician: You get to go deeper and deeper and deeper.
I wish synthesizers were as expressive; as a guitar player you could do so much more with the same instrument, which makes it so much fun exploring and learning every single time you pick up the guitar.
The whole interview is here.