The thing about motivation is that it presupposes itself. In other words, it cannot be created unless it already is there. (Of course, there is external motivation. If I said I would give you 10M dollars to publish an article in the Hispanic Review, you could probably get "motivated" enough to try and do it.)
So the trick of motivation is to realize that it is already there. To identify completely and unequivocally with the enterprise in which you are engaged. This means the process and the ultimate goals become one seamless, gapless whole.
Motivation should not be a problem but it is, often. If I do not go to the gym today it will because my claim to want a more perfect physique is just that, a claim. Or I could convince myself that my physique is fine already, etc...
I was confused as a kid by the notion of "self-control." Just who was this other self who was supposed to control the self? Was I two people. When I had an outburst I was criticized for, I knew that I had chosen this behavior, and hence was controlling myself. I'm still a bit confused by the notion of one part of a self controlling another part. Suppose it is 10 p.m. and I am feeling lazy and don't want to get beer at the store. But I also want to drink beer. I could be proud of my supposed "self-discipline" either way, whether I go get the beer or not. Ultimately, though, it is about what I actually want to do more. My actions are a good guide to that, more than what I say I want.