People sometimes take the expectations of realism to ridiculous levels. I will tell outright: even the optional, very-high-detail Last Gasp rules don't properly model the differences between running a sprint, a mid-distance run, and a marathon.
But in general, you can expect some sort of approximate-order-of-magnitude reasonableness for many (but of course not all) phenomena, where by knowing the input parameters you can often get at least a general idea of reasonable-ish outcomes.
Those can, of course, be adjusted by adjusting the rules if one wants to emulate certain genres. Like mild chanbara allowing combat jumps to effectively be double the normal distance (for a simplistic example).
All of the above of course comes with a predisposition towards the system having a lot of moving parts.
They're usually well-defined, but there's lots of them.
Well, well-defined by RPG comparisons.
And when I write 'lots', I do mean lots. Like over a hundred skills, most of which are only needed for certain character concepts. Or many dozens of traits, each with special optional modifiers that adjust how they work.
This can be a boon and a drawback.
It's a boon in the sense of 'I have an idea, and the system already has something to help me flesh it out, often with implicit or explicit worked examples'.
But it's a drawback because it can be hard to grasp everything right away. And while some traits' synergies make sense, others are mere side effects of the design process, essentially bugs.
And there's also the fact that adjusting things like trait costs for a specific campaign can result in cascade effects due to the sheer number of possible interactions.
(By traits I mean everything - attribute, secondary characteristics, dis/advantages, skills, techniques.)
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On the other hand we have the FATE family of games, which don't focus on the above sorts of input-system-output pipes. They also have fewer moving parts.
You have no functions that you can use to figure out an outcome or reasonable range of outcomes either for a genreless or a given-genre situation.
You, GM/table, have to do it all in your head, and assign difficulties based on that.
Or assign meanings of success/failure/tie/complication.
Another consideration is that FATE-family games tend to have a very loosely defined 'pool of possible traits'.
There's the Default Skill List (which is pretty cool as far as skill lists go in universal game systems!) which you can mostly keep as-is, but Aspects are very freeform, and Stunts are meant to often be customised or also freeform-invented a lot.
This can be a boon and a drawback.
The description of a flask of oil says:
You can also pour a flask of oil on the ground to cover a 5-foot-square area, provided that the surface is level.
When playing on a grid, can I pour a flask of oil on any adjacent square or just on the one I am standing on?
I've recently noticed a couple questions that seemed like "make me some suggestions for this homebrew idea I had". I voted to close both as an off-topic Shopping/Recommendation request, as to me they both seemed like asking for recommendations and idea generation, which is clearly off-topic here....
