Well, from what I've learned and experienced, the mind will only let you be motivated if the end result has some intrinsic value. Examples being mowing people's lawns in return for money(positive motivation), or putting on your seat belt because you don't want to die(negative motivation). Okay, that last one could also be viewed as positive, but the point is death is something bad you don't want to happen to you.
From this I derived a few things that help me: When I start a project, I visualize just how awesome it's going to be. Everyone's going to love it, I'll have learned a lot, and I'll feel good. Now, I want that. That's positively motivating me to get off my ass. However, it's inevitable at this point in my life(I'm slowly trying to kill it) that laziness and procrastination sets in. To kind of kill that, I think about how my life is so finite, and that sitting around being unproductive is not a neutral state. It's not moving me forward, so it's counter-productive. I'm wasting time that I could be learning things and working towards becoming better, at whatever it is. Now, I don't want to be counter-productive, so even if I don't continue with this specific project at the moment, I'll still go do something else productive. This all helps to varying degrees of course, and it's not always helpful but most of the time it gets me back in gear. I will tell you though that positive motivation is way stronger than negative.
For where you are now, I'd say re-think it a bit. Remember why you wanted to start this project in the first place, and visualize just how awesome it's going to be. Break everything into chunks, and break the chunks into smaller chunks, and do them. That's how I complete large-scale projects.
I started this project so I could make a platformer game with it, and if I quit now I won't be able to even start programming the game...which means I'll have literally wasted a month of my life doing this.
No. That's a counter-productive frame of mind. Just because you didn't finish it doesn't mean you wasted your time. All of the time you spent on it so far, you've been thinking about things, whatever they were and you've been learning and developing your own way of doing things. That's not a waste of time. Even if your motivation runs out for the moment, it's totally okay. Maybe one day you'll get a spark and go back to that project, and refine it to completion. Maybe not, maybe you'll move on to bigger and better things. But it's bad that you move on, it just means that you moved on. But I hope you do complete this, it's a good habit to finish something every now and then.