COURAGE, the cowardly dog and the secret ingredient.
Making any sort of change takes an ounce or two of bravery. You know that, because those fitness/life changes you've thought about but haven't made are sitting there licking their lips and twiddling their thumbs, looming in the distance, reminding you of what you haven't done yet, which is at the very least intimidating, if not downright terrifying.
Hoards of advice would tell you to just do it anyway, that the only way to get started is to start, that the time is passing by no matter what so you might as well get to stepping. I don't disagree, and also... if you were gonna get started after hearing all that, you would've done it already ("you," is really, "we," here).
The fear will never disappear entirely, so, what then?