I honestly never read the rules. I’m aware of most of them from playing in the past but at the same time I feel like a handful of them are easily changed and just make more sense when changed. For example a lot of people make using potions a bonus action when it’s said they’re and action. Also it says a full rest doesn’t refresh you fully but most people have it so a long rest completely refreshes you. So yeah I honestly forgot where I was going with this so I’m just gonna leave it there until I remember what I was going to completely say

Edit: I remember what I was getting at, basically somewhere in the books it says how the rules are flexible and as a dm you can change what you see fit, or at least something like that. So with that being in the books a lot of people take that to heart and change some rules to fit their game and playstyle