When people say "children can be cruel", they are talking about child-on-child meanness. Kids can be horrible to each other - the playground is where your personality is forged in a cauldron of hair-pulling, name-calling and dead legs.
But when you have survived this and made it through to adulthood, you think it is behind you. What I didn't realise was that children save the very worst for their parents.
Last week I tore a tendon in my shoulder and the pain was really very bad. I would say definitely worse than childbirth, but in the event of first-hand confirmation being unlikely, I'll have to settle for probably worse than childbirth.
My wife was sympathetic and, despite being somewhere between lightly and heavily pregnant, she womanfully took over all the heavy lifting. My daughter saw my weakened state as an opportunity.
We often enjoy a friendly wrestle, and having a slight weight advantage, the onus is on me to take it easy. But when she saw me protecting my right shoulder no such quarter was given. She was going in hard and aiming for the injury like a boxer targeting a cut above an opponent's eye.
And when we were out for a walk she really turned the screw. Normally she acts the big girl, refusing to hold my hand and scootering off ahead. But suddenly she was a baby again, wanting to be carried every step of the way.
At one point I stopped and, with the breath of defeat blowing away the last remnants of my pride, asked if she wouldn't mind walking the last 50 yards to the playground because I was in a lot of pain. "I can't," she said. "It is too far away and I am tired".
I tried calling her bluff by walking ahead and leaving her behind. But after a few paces I looked back to see her sitting on the floor with the face of a poker player who knew my flush was never anything other than busted.
At this stage I could have been walking on bloodied stumps over broken glass and it wouldn't have troubled her conscience one bit.
I scooped her up in my good arm, but this wouldn't do. She swivelled deftly around my body until I was forced to take her weight in the most painful way possible, before saying with quiet satisfaction: "Yes. Daddy carry me like this!"
Then of course when we got to the playground she was no longer tired and ran up and down in a calculated taunt to the serf who had lugged her there.
I don't mean to say that she is in any way a mean child. She is a very nice child. To everyone else. But I am her father and I am not allowed to show weakness. And if I do, she will punish me.
And this is far worse than the cruelty children show to each other. If you are a child and another child is mean to you, at least you have a chance of getting back at them. When you are an adult, you just have to take it.
Or do you? I am almost fully recovered now. And when I'm 100 per cent fit, I'm going to take her down.