Because there's no such thing. You make the rules as you go along. I think about how our friends raise their kids. Then I go with what I feel is right. No one ever said it was going to be easy.
Kids are people, too.
But I try to cut my kids some slack, especially the older ones. Sure, I want to keep them from making the mistakes I did, but you can only give them the foundation they need to build on. Have an open-door policy. My kids can talk to me about anything, any time. I make sure they know that.