It reminds me of the quote,"As a parent, the odds you'll screw up your kid are 100%"
What no one ever told me is that you are a first-time parent every year. Just when you get the hang of taking care of a four-year-old, they turn five. And no matter how many kids you have, the next four-year-old is nothing like the last one.
But you're right. My parents were both teachers, and they'd say, "Parents come in and shout, 'You're with my kid eight hours a day. Why can't you fix this?" To which they would think, "Because you're with them the other 16."