It shouldn't be surprising. Most, if not all of us, are our own worst critics. Naturally, it would then carry into parenthood. Even amplify it. Because suddenly, here is a little person in our lives that we love more than ourselves, and to attempt to be the person they need us to be, we hold ourselves at an impossible standard.
A lot of people also do that to other parents. We judge other people around us constantly, parents or not. Sometimes, it's within reason. When you see a parent spanking their kids in a store, or a parent yelling at their child, or a couple having an argument in public where one of them is being obviously cruel to another. But often times, it goes way too far, to all the little things. Sometimes even holding others up to an impossible standard we don't even hold ourselves to: expecting other people to be perfect. Even worse, expecting people to be just like us. Judging a mom for formula feeding, or for breastfeeding in public, or for not breastfeeding in public... for not having the nicest things, or spoiling their kids too much by giving them whatever they want when they throw a tantrum... the list goes on and on. But the truth is, when we do this, we sometimes need to stop and think. This might not be an everyday thing for them, maybe there's a special circumstance, we just don't know. Maybe they're just having a bad day. Hey, I've had some of those, myself. I'll just cut them some slack, like I wish other parents would do for me. And even if not, every parent has the right to do what they think is best for their children, and what works for them and their kids (again, within reason---extreme or illegal things obviously don't count).
I'm going to go out on a limb here, and say that most parents are like me in being the opposite of the above description. We cut all the slack for your friends, family, or even people we just see on the street or in the mall---without ever giving ourselves a break. Parenthood can naturally have that affect on people, considering so many of us (if not all of us) realize how very helpless and clueless we are when our little ones come into the world. From then on, all of our time is spent worrying that we've made some irreversible mistake that will change our children for the worst. Forever. It becomes like this with everything. I'm inclined to believe this is not the case for some or many Europeans, but it is a tiresome reality for many of us who are parents here in North America.
I had one of those moments a few days ago. My son had a little fall yesterday while under my watch, and I felt absolutely dreadful. I felt that it was inexcusable. He was in pain, and it was all my fault. I was still feeling awful about it the next morning, and asked my mother if a similar accident had happened with me or any of my four siblings when we were little. She told me of a few examples, and I felt much better. I had to remind myself: To err is human, and I am human.
There will be (metaphorical and literal) bumps along the road. You can set preventative measures in place, and sometimes, despite your best efforts, things will still happen. When they do, give yourself a minute to worry yourself sick to get it out of your system. Then take a deep breath, and remember that it has already happened, and freakout out doesn't help the situation. The best thing you can do is calm down, so that your little one can tell you are calm and that they shouldn't worry themselves either. Keep it in mind for all of the little bumps in the road the future will bring. Keep calm and carry on.