My experience as someone who (probably) has ADD and who knows lots of people who do, is that ADD people tend to be highly passionate and motivated. It's just that our motivations jump around all over the place.

For a long time my response to this tendency was to try to control, direct, pin down my motivation so that I could stick with something until it was done. Doing this caused me to actually have a real deficit of motivation, instead of just an always-changing motivation. Once I stopped trying to control it and embraced jumping-around, following my interest wherever it led me, I actually had much more success seeing tasks through to completion (and even circling back to ones I'd left behind, because I wasn't feeling guilty about having left them behind). It's like my attention is highly fragmented, but I still have the same amount.

An ADD person's motivation is like a wild animal that you just have to give room to so it can do its thing. Hitch a ride to it, instead of trying to tame it, and you'll eventually get where you want to go.