[dv_dt]

Fluids is a pretty good metaphor, but I would say that today we have sufficiently good reproducible physical understanding of fluids that we can generally fly airplanes at a high level of certainty (e.g. turbulence on the wings is both predictable and controlled in the correct ways that the plane does not crash). In comparison we crash the economy and even sub portions of markets periodically (and the last general crash was worse than many previous recessions) - we don't even have a complete picture of which turbulent areas to be wary of economically.

Or to maybe to a more human point, we can carry humans around on airplanes just fine, but don't know how to carry a payload of a nation of humans on a stable and healthy economic vehicle.