I think that the main problem with thinking you have prepared for anything, before your first baby arrives, is that the baby almost never reads your plans - and if they do read them, they give a wicked laugh, and then set about ruining every one of your carefully made plans!
Same goes for baby books - they are great, but babies never read or follow instruction manuals! My favourite baby book, and the only one I recommend, is "How Not To Be A Perfect Mother" by Libby Purves - written from her own experience and the experience of her friends, at the coal face of motherhood, it advocates taking away the pressure to be perfect - as she says, even a perfect madonna-type mother needs 20 minutes off, with her feet up and a drink. And what matters is that the baby is clean, fed, warm and happy - and if that means they are wearing nothing but a disposable nappy and one of their older brother's jumpers with the arms rolled up, it is fine.
I honestly think that the pressure I put on myself to be a perfect mother helped push me into post natal depression. I had this image of myself as a mum, and how good I was going to be at it, and when things didn't work out, it made me depressed. Breastfeeding was the biggest thing that did this for me - I so wanted to breastfeed - I went to the NCT classes and was utterly committed to it, but it never worked out with any of my three dc, and I beat myself up so badly about that.
I think planning is good - it helps us feel in control of a new situation - but we need to be realistic too, and to go into parenthood knowing that we can't control everything, and that our best-laid plans may come to nothing - but as @KingLooieCatz says, even when it doesn't go to plan it can still go well. Having small children is, in my experience, a chaotic whirlwind of ups and downs. But the ups definitely outnumber the downs, and you can learn to live with the chaos, and tame it to some extent - and to enjoy it all. But if you are too wedded to your vision of how things should be, you may find it hard to be flexible - and being flexible is key to parenthood, I think.
Sorry - that was a bit of an essay. I hope it made sense..
TL:DR - children laugh at our best laid plans so best to be flexible.