Motivation is great. Being excited to do something makes it so much easier to do. Its easy to get things done when you are excited to do them. Motivation and enthusiasm are fantastic to get you started on a project, but enthusiasm wanes and motivation fluctuates. Motivation comes in bursts, and is generally pretty fragile. I find that I can affect my motivation listening to music, or watching videos, and lose it with just the smallest of setbacks. I would wager that every project that was leapt into and then abandoned was based on motivation.
Willpower will also only take you so far. Willpower is like a muscle, it can be used only so much before it wears out, loses strength, and fails. Relying on willpower is risky, because most people can not predict when it will run out.
If you want to succeed, if you truly want to get things done, you need discipline. Discipline is what drives you when you don’t want to do something, we all know this, but discipline can be applied to much more.
A couple days ago, I crashed my mountain bike quite impressively. I came off a narrow bridge across a ditch, and went (literally) face first into the bank on the other side, roughed myself up pretty good. Bent my glasses, scabs on my face, a fat lip, and a very sore neck.
Discipline kept me out of the gym.
Discipline is just as much about not doing things as doing them, and should also be applied to moderation and balance. In regard to fitness, discipline is also about recovery, whether that recovery is rest days after working out, or allowing yourself time to heal after an injury. Moderation, balance, and recovery require as much discipline as consistency and follow through.
Without discipline, most projects in life, be they fitness or financial, are doomed to failure. So find those things that motivate you; strengthen your willpower; but above all, develop and apply discipline.
Do this and your goals will be achieved.