People are interpreting the question as generally "what's something you wish you started doing sooner", which is similar and more commonly asked. People in the reddit thread did this also.

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.