So many things in FF7, 8 and 9. I'm sure other FF's are guilty as well, but Square was absolutely trying to sell strategy guides back in the day with some of the ridiculous things that were nearly impossible to figure out on your own. Even if you stumbled across a few of the things, there were dozens of other missables throughout the games that you would almost certainly not find.
I don't miss those days tbh. I used to think that was a great feature of old school gaming, but my OCD brain really hates stuff like that these days.