Hm. Let's see if I can make all this make sense.
I am not sure if I could be sincerely called gifted or not. I'm not one of those people who just coasted through high school doing nothing. A lot of people characterize giftedness as needing to do absolutely no work, and that's not me. Rather, I'll say that I couldn't get through 14 AP tests (12 5's, 2 4's--just to say that I wasn't getting 1's or something) with no work. That took a lot of slogging. I've always needed to think about things with care.
For a long time, though, I can't really say I was motivated to work hard. I worked hard, but not as hard as I could. I realized a year or so ago, though, that I saw mathematics as my true calling, and started working a little bit. Now I'm trying to move up to 14-hour days of study, step by step, with the hope that I'll eventually stop having dysfunctional brain-crashes after the 8-hour mark. My motivation is not only my dream, but the realization that I'm truly capable of doing something. It's the knowledge that, in a world that is difficult for me to navigate, I can do this one thing and everything will be clearer. I can get everything I ever wanted from this subject, and nowhere else.
So you ask yourself: what's your dream? And then you follow that dream for a while. If you give it up, it wasn't the right dream. No matter. Just need to find the next one and coast along on that until you know. It's a little bit like falling in love.
Nowadays, I put my hair up and dress up like a school marm from the 1900s to remind myself that this is Serious Business. I go to the library every day at 9 and stay there until 6, leaving for the occasional class. Lunch break is from 12:00-12:30, when I eat and spend a couple minutes goofing off online. Every time I want to quit, I remember who I am and what I'm fighting for, and then I keep going. When the choice is between "sit in one place doing nothing for nine hours" and "do that work I really want to put off," it's very easy. I work, and I work, and at the end of the day I feel good for working so hard--but I still want to work even harder.