Strangely enough, I think I do understand. As near as I can tell, life's two greatest pleasures are 1. Love (both loving and being loved) 2. Voluntary hardship

I mean, what is parenthood if not love and voluntary hardship?

On the other hand, I think you are describing your subjective experience. I've talked with some "one-and-done" parents who deeply love their child, but wouldn't want another one if you paid them.