Everyone is different. Some people struggle with pregnancy. Some people sail through. Same with childbirth, same with newborns, older babies, toddlers etc. Sometimes that's because of specific things (illness etc), and sometimes the stage just isn't your preference.
So I found the newborn phase fab, and a breeze, but to some, it's the trickiest time. Part of that may be due to them, or the child, but also some people prefer it, in the same way we people prefer dogs to cats or vice versa.
So don't judge yourself or others if you find something tricky, thst others find hard, or vice versa.
Oh, and they are quite hard to kill, so accidentally using adult shampoo, or realising that you gave 3ml of calpol not 2.5ml accidentally isn't going to cause any harm. I'm not saying be negligent obviously, but that they are more resilient than you realise, and if you have a second, chances are you'll really find that out... Basically, if you can be a relaxed second child parent if a firstborn, then you save yourself a lot of worry.