@ArabellaScott I think this is really the crux of it:
Nobody can ever fully know beforehand, though. You cannot 'inform' yourself of something so deeply unknowable. There is almost no way of knowing how things will unfold. Much is luck. We can make a rough guess, but nobody can know how their pregnancy, birth, post natal expwriences will be, how easy/hard/healthy their baby/child will be, what cicrumstances will play out with work, partner, health, etc.
I think often the shock about "not being told" how hard it would be comes because we have so little control over the temperament of our child. And that has such a huge impact on our mothering experience. That's relatively unusual for most decisions that we make. Generally speaking, at least in Western middle class circles, we can be pretty sure that if we put our minds to something we can achieve it (running a marathon, getting a job, learning a language) and that the outcome is roughly proportional to the effort exerted. But, in the same way you can't just effort your way out of birth trauma, you can't just work harder at parenting and get a child who is easy to parent.
I assumed that nurture and parenting style would have a much bigger impact than it actually seems to. So we hear stories of other mothers finding it extremely tough with various things (sleep, breastfeeding, weaning, tantrums). But we also hear of other parents who don't have these difficulties. And we know there are strategies and parenting techniques to deal with things. So it seems like by reading the right books and applying the strategies well and being loving and kind and gentle, we will have a lot of control over how our child behaves, how and when they sleep, what they eat, how they settle at school etc. (See also childbirth!)
Of course, there are parenting strategies that are genuinely helpful, but babies and children start at such different places with all kinds of different strengths and difficulties that it makes it almost meaningless when considering whether to have a baby. As a case in point, a colleague has 2 children who both slept through the night consistently from a young age and are totally happy to be left with a sitter. They are calm and play well independently. These are skills my DS is still developing at nearly 4 (and I haven't just passively waited for change, I have put in a lot of effort)!
Our experiences of parenting are absolutely poles apart. There was no way to predict this ahead of time. But if I was a prospective mother hearing both our experiences, I would probably think something like "Well there's no way I'm being like that sucker. She must have done something wrong. There's no way my child will be like that."