Hi Bartholemew.The only motivation I've ever had to practice or play any instrument is the sheer joy I get from it. Practicing specific songs for a concert is a different thing. That's my job, and I'm much more disciplined.
If I had a lotta bucks, I'd probably never go on a stage again, but I'd still play constantly (alone, or for anyone who'd listen) 'cause I love it.
Rick