... is something my High School Bible teacher used to say, and it's a pretty good way to approach parenting.
That's another thing that surprised me about parenting. It isn't so much about enforcing obedience per se as it is about teaching good decision making. Life has its own consequences for making bad choices, and you want to give your children the discretion to avoid them when possible.
Part of parenting is creating artificial consequences and decisions along the way that are a lot less severe than Life's consequences. A punishment should not be a threat ("if you don't do x then y will happen to you") but a choice ("you can choose either x or y. Life will be easier for you if you choose x.").
In some ways this is just semantic, but I think it makes a difference. It emphasizes the child's autonomy. I'm not trying to force them to do what I tell them to. I'm just letting them know that life will be harder if they don't than if they do.
Now, children are smart. They know these boundaries are artificial, that they are imposed by us and we could change them if we chose (hence the whining). But they have a harder time realizing that some boundaries aren't artificial. If my kids are upset about something that is totally outside any of our control, it does no good to explain this to them. Sometimes when my kids are complaining about some discipline I say in jest "don't blame me, I don't make the rules". Of course I do and they know it, but I'm trying to communicate in a silly way that this is a part of the world that isn't going to change even though they want it to. And that's a much easier letdown than discovering the hard way that life is hard when you're stupid.