The other 51% of the time is the greatest ecstasy that you will ever feel. There is something very rewarding (and almost equally as devastating) as knowing that you are largely in charge of a person's destiny, or at least in giving them the tools to fulfill their own destiny. Nothing is more fun than imaging the potential your child has, and the happiness you feel when you teach them a skill or inspire progress in some way. I'm still a young father who has yet to experience the other side of that coin; I dread the day when I'm bound to do something that scars him for life.
I have frequently caught myself throwing an arm or even my whole body in front of him when a car passes, or there is a loud noise. I deny him certain things he wants out of nothing more than white-knuckled resistance and a belief that I'm serving his best interest, then stifle a laugh when he throws an absurd fit. Every moment of every day is a tightrope walk between what one should do, and what one shouldn't do at any given moment, and the knowledge that no matter what I do, there will be mistakes along the way.
About 2 years ago I wrote a blog about love and parenting opining about the intensity of love a parent feels to a child. It was written before I was a parent, and only shortly after starting the adoption process. Now, after being a father for a little over a year, my ability to write has gone down hill but I can speak a little more concretely about my experience of parental love.