Motivation can help, but Motivation is short lived and may only last a few days. Discipline is like a muscle. The more you build it, the more you can rely on it. Everyone has some discipline (can you hold your breath?), but not everyone develops it.

Basically it comes down to taking on little challenges, conquering them, and gradually progressing to bigger ones. Its like progressive weight training. As your self-discipline gets stronger, a challenge like getting out of bed at a certain time will eventually become trivially easy. But if your self-discipline has atrophied, it can seem an almost insurmountable hurdle.