Inclusio Unius Est Exclusio Alterius

This is a legal term that means roughly: to incluse one thing is to exclude another. To put it another way, when it comes to lists of things in statutes or rules, the list itself excludes alternative ideas which are not on the list. To include is to exclude. 

This is part of why I don't like 3.x style feats & 4th Edition style powers in practice. The more things you roll into the idea of a class of an enumerated feat/power the less idea space you leave for people to just wing it in play. 

This is one thing I think the OSR gets right with minimalist rules systems. It leaves the mental space open for on the fly rulings at the table, minimizing the battles between GM & a rules lawyer. 

Now, I've played a ton of 3.x, Pathfinder 1e, & 4th Edition. When the designers make a thing like the feat Cleave, only characters with the feat can do the things that feat says. In 4th Edition, once the dailies & encounters were expended there was a feeling that you were left to helplessly flail with at-will abilities because you felt like there wasn't anything else mechanically you could do. 

I loved those games but that was frustrating as a player. 

I actually like ideas like the stunt mechanic in AGE games. It moves those discrete mechanics off the character sheet, out of the class, & into a place where anyone can theoretically reach. It's not a flawless idea but it does make me think of ways to improve along those lines.