I love the Yale Commitment Essay Question! It brings up such interesting stuff. And yes, we've seen great outcomes with personal stories for this essay, but the most effective 'commitment' stories are commitments that can be tested and measured. Otherwise they can read more like New Year's Resolutions; easy to make, easy to break.
So your personal life decision needs to be one that has had enough time to develop, so that we can see how it's going, what challenges to your commitment came up over the last couple of years, and so on. To that end, I like to see a commitment that has either been going on for at least two years, or that has required you to make a major tangible change in life as well, such as a relocation or job change, something where you 'put your money where your mouth is,' so to speak.
Good luck!
Margaret Strother