I think, looking back to when DS was a baby, that it wasn't so much hard as unpredictable.
For example, just when I thought I had nap time sussed he grew out of that phase and dropped one nap. Which threw me for a few weeks, which made things stressful until I adjusted as I was still on 'old time'. Everything with a baby is baby led. They don't 'fit' around your day, your day fits around them.
After a while you figure out that making a sandwich in the, hopefully, little nap they're having (even if that is at 10am) or even the night before and putting it in the fridge means you'll get some chance to eat.
Because if you don't, DS/DD will need feeding just as you start to make the sandwich and of course will take longer than usual to finish, or have chronic wind (even if they're not prone to it) as soon as you start to eat and will take hours to bring it up and stop crying, or need a nappy change (at least twice) in 15 minutes just as you've made a cup of tea.
It's because it's all new all the time. You get one thing sussed and they change because they grow. Even if you've had kids as every child is different and you're not in their rhythm. You soon learn not to fight it - they don't 'fit' so you have to. It's like relearning your job every few weeks with little 'tweaks' changing all the things you used to do.
And when they're toddlers you need a new strategy. It's like preparing for a NATO troop movement just to get them out of the door sometimes. Nappies, lots of them because you can guarantee a toddler that normally uses 3 nappies will need 6 if you venture out of the door - it's an inbuilt chip! Snacks because you will never find somewhere that sells anything other than avocado and hummus sandwiches if you take a toddler out without snacks (it's an unwritten rule) and a change of clothes - because the child who never vomits will be like something out of The Exorcist as soon as you venture near a soft play area.
So hard? Not always, but often unpredictable.