It is interesting that this discussion is mainly centering around combat. that fact says something about the assumptions of what an RPG is, here at least.
Let's presume, though, a game in which combat is very rare or non existent. Let's use X-Files as an example, because it is probably well known to most, had relatively little "action" and was a procedural so it has an understandable play loop.
In this hypothetical X-Files game, you define your character with a few bried statements that kind of serve as Fate aspects: what law enforcement branch you started your career in (National Park Rangers), for example, then something about a relevant interest or hobby (hunting) and then a disadvantage or "trouble" (medical debt from a now deceased spouse). That's the sum total of your character, aside from the presumption that you are a competent investigator.
Gameplay revolves around solving mysteries by examining crime scene and interviewing subjects and researching archives and stuff. Sometimes when you declare an action, the GM calls for a roll of 2 six sided dice, which you add together and tell the GM the result and then play continues.
The question is, do you need to know any more than that to play this game? Do you need to know what the range of Target Numbers are, or how your "aspects" interact with those dice rolls? Do you need to know what stats your sidearm has?