Your last paragraph reminds me of the following series of YouTube videos that goes over how to build a "correct" fluid simulation, starting at the quantum mechanical level (iirc): https://www.youtube.com/playlist?list=PLMoTR49uj6ld32zLVWmcGXaW7w2ey7Vh4.

Multiple scales of complexity and interaction, that's way too computationally intensive to just directly stimulate how reality works, and so each scale has to be carefully "averaged out", in a sense, to end up with a simulation that is cheap enough to run yet still behaves realistically and reproduces as many nuances as possible.