Warning: Running analogy to follow. (I know, you're not surprised.)
A friend of mine says that she runs races not only for the thrill of the race, but to make herself exercise. And I can attest that there's nothing like a looming race to get you out to train, even when you really don't want to.
Some of you may know that I ran a relay race a week ago (184 miles with a team of 12), and several days before the race I knew I had to run. The upcoming race hovered menacingly over me, but I didn't want to do it. I really didn't want to. However, my stubborn will dragged my reluctant self outside and we went for a run. (Do you like the use of the royal "we?") And you know what? After 1/2 mile, I hit my groove, began to enjoy myself, and I was glad I did it. Oh, I'm sorry. I mean, after 1/2 mile, we hit our groove and began to enjoy ourselves.
*cringe* Forget the royal "we." Now back to the point...
Let me tell you a little secret: this scenario plays out to some degree every time I go to exercise. Getting started is always hard, but once I get going it's easier to keep going.
Dictionary definition: Inertia is the resistance of any physical object to a change in its state of motion.
And I think that mental, emotional, and motivational inertia is even harder than physical inertia. One of the biggest hurdles in achieving goals--no matter in what area of life--is overcoming that internal resistance.
So just get your butt moving, because that's half the battle.