Question

In hydrostatic energy transfer, what causes the "load/mass" to move? Pressure or Flow?

Answer 1

I think it is pressure, which causes force on the mass to move it.
But the pressure is because of the flow of the fluid.

Answer 2

"But the pressure is because of the flow of the fluid.", isn't that contradictory, to "I think it is pressure, which causes force on the mass to move it." ??
The flowing fluid have its own mass that also need force to move!?