Oh yeah fluids are cursed. Fluid simulations come in two varieties: accurate ones that barely last as long as your question and then explode, or ones with so many weird little hacks added to stop it from exploding that you can no longer be sure if it's accurate anymore.

Then after fluids there's air. Aerodynamics is still such a dark art, even with windtunnels and computer simulations. Like if certain Formula one teams or aerospace companies were to lose one or two key figures that somehow seem to be able to see air particles, they'd be screwed.