At the time of not knowing we can't worry over what we don't know as we blissfully go on our ignorant way; it's afterwards that we get informed of what we didn't know and by then it's too late to feel bad over it.
To answer your question:
1. To learn of some things my children did when they were young and away from my watchful eye. I learned because they told me as grownups. Nothing illegal only dangerous and if I had known then I would have been frantic.
2. That smoking caused cancer
3. That my country during World War II was right in every thing they did
4. That my parents were only there for me and my brother and had no need for a llife of their own.
5. Etc., and etc.