I didn't realize I should have been using him as a a role model until he passed away, but when it happened, it was very powerful.
It is also the first death of a relative I've had to deal with in my life.
Death often has that effect, for sure--it's painful, but can be inspirational at the same time.
If you had asked me without a scale for reference, I would have said 160 pounds.
It was 172.
172 isn't a crazy weight, but not realizing I'd made it into the 170s (which I'd never been before) while simultaneously believing I was 12 pounds lighter was definitely a "moment".
After a month of very low carb diet, exercise, and other lifestyle changes, I'm down to 153 and feel much better too. :)
What you're really after is more like "what is a moment in your life that made you rethink things and change your behavior".
I think they're both valid interpretations of the question. There's a common idiom, "an aha! moment", which can refer to either the source of the revelation or the revelation itself.
Ugh.
Edit
I've asked a few people to describe their moments instead of just listing what the change was. YMMV, but for me, these are far far more interesting than random lists of things.
I may have mis-interpreted the OP's intent, but it sure seems a lot more compelling when you know the catalyst as well as the reaction.