Add me to the No Curfew Club.
I had very few rules growing up because I was a "good kid." I wasn't interested in partying and sneaking off with boys or other stereotypical teen activities. I loved going for walks and was annoyed at the "no walks after dark" rule. I was too boneheaded to understand what could happen to a kid out walking the streets by herself in the dark but am grateful for that rule now.
The biggest "aha" moment I've had as an adult is the rule that you speak to everyone when you come into a room. I thought it was totally stupid and unnecessary to have to greet and hug everyone individually. Once when I was 14, I ran into the house and bolted straight to the bathroom because I had to go so badly. I said hurried "Hi" to my dog (who was in my direct line of sight) but not to my dad who had been sitting in the corner. The second I came out of the bathroom, I was grounded. It seemed so harsh and unfair. But as an adult, I can only imagine how it felt to have your youngest child greet the dog and not you. My dad and I had a seriously strained relationship during my teens but, even with the things he'd done, he didn't deserve that. I now understand the common courtesy of acknowledging someone's presence because I now know how it feels to have someone say hello to a select few people and pass you like you're not even there.