What I do know: until I started treatment for ADD, the entire concept of "willpower" or "motivation" just didn't make sense to me. It was something other people had, maybe; or perhaps they were lying. But with treatment, "motivating myself" into doing things for merely their effects on my long-term goals is a perfectly obvious thing to do. It's very similar to what it felt like to go through puberty and gain a sex drive—but what I've gained is a drive to succeed in life.
Watching my own behaviour, introspectively, is fascinating. I keep expecting to hear a little voice that says "eh, that's too much effort; it makes me tired just to think of doing that." That voice was a persistent companion for most of my life. Now, that voice is just not there.