By now, the vast majority of New Year's resolutions have failed. It's a recurring theme. State an ambitious goal, make a plan, start with enthusiasm...and fade. The problem lies in using the goal as the target. And the size of the goal doesn't matter much. Whether it's 10 pounds or 50 is incidental. There's a good chance we won't lose all of the weight not because the goal is too aggressive, but because the focus is on the outcome, not what it takes to get there.
The resolve should be centered on habit forming. And furthermore, it should begin with really small habits, which eventually will lead to bigger ones. Want to run a first marathon in the upcoming year having not run more than a mile since grade school? The marathon shouldn't be the resolution. Forming habits to become a runner should be the resolution. Then, start small. Put on sneakers every morning at 5:30 am and walk to the mail box. Every day, without fail, rain, snow or shine. Do this every day and you'll be walker. Then, you can add in running. Over time, you'll be a runner. And if nothing else, you'll be sure to check your mail.
Goals are important. Who we become is more important. We become what we do, day after day.