There's one thing that nobody ever told me before I became a father, so I'll post it here: I was (and remain) shocked by how much
fun it is.
Seriously. My wife and I were married for 8 years before we even decided to have kids, and didn't do so lightly. What convinced me was a fairly abstract idea that it was, like birth and death, something more or less fundamental to the experience of being a living, biological creature, and though I likely would be happy either way, it seemed like I should go for it given that this was my only chance. "Buy the ticket, take the ride."
I saw a lot of data purporting to show how bad parenthood is for self-reported happiness, especially for dads. And I heard from my friends who had kids (when I could talk to them, which was rarely, since they basically dropped off the map once the kids came) how rough the sleep deprivation was, how they never had time to work out, see their friends (or, half the time, spouses), do fun things, etc. And I figured I was in for something that would basically suck in the near term but had a high chance of being, long-term "rewarding" in a vague, hard-to-define-but-nevertheless-really-important kind of way.
This was completely wrong.
Of course it sucks to never get enough sleep, of course it's a bummer to lose time for all the things we have always enjoyed in life etc ... but the sheer fun of it has outweighed that for me at every turn. Just hearing that kid's little voice makes me smile, and I've never had so many reasons to laugh as I have since he's been born.
This isn't a pitch. I am pro-humans and pro-more-humans and I think the HN crowd is above the median so on average I'd be happy to have everyone here have a bunch of kids, thus raising the intelligence waterline and producing a better future etc. But I don't claim to have any idea whether it's right for you in particular, and wouldn't have any idea where to start in figuring that out.
But on the scale of "things they don't tell you", the biggest surprise in my life was just how enjoyable the first few years of my son's life have been. YMMV but I figured this was worth posting since nobody told me, and I might have been happier going in if someone had.