Does Persona 5 do that thing where to get the best ending or significant content you need to be following a guide?
I had to play P4:Golden twice because I saved over my file after getting a non-true ending.
Playing 999 recently highlighted that it's a common feature of older style Japanese games.
Very mild, but spoiler tagging just in case:
There is exactly one conversation where you have to choose the right answers, and the game warns you that it's important beforehand. Keep a separate file just to be safe, but don't worry about it too much.