'Life knowledge' and 'school knowledge' are two different things. While you're in the education system, you'll learn all about complicated mathematical equations, the periodic table, chemical formulas and focused areas of history. Unless you go into one of those fields, you'll never use that knowledge again. It eventually gets replaced in your brain by more important information, like how to operate a spreadsheet.
That has the unfortunate consequence of making you seem stupid when your child wants help with their homework. You might vaguely remember being taught the same things when you were at school, but you can't remember how to do them. Now you look like an idiot in front of your child because you can't remember how PEDMAS works, or the principles behind long division. How embarrassing! Maybe it's time to take an adult learning course, just to avoid the shame.