Practicing can be like having sex with your significant other. You don't really want to start it all the time, but once you get going you wonder why you don't do it all day long.
I just tell myself "You only have to pick up the bass. If you stand up with it and then you want to put it down immediately and get back in bed, that's okay." Once I pick it up, I never put it back down before at least a half hour or so is up.
I do the same thing for riding my exercise bike. "You only have to ride the bike for five minutes. If you don't like it, you can stop." Once I get going, I always do the whole workout.