Fluids are shapeless.
When a force is applied to a fluid, the pressure increases, but whereas the force is directional, the pressure is omnidirectional . Consider the force applied to the surface of a glass of water by the atmosphere. That force is downward, but the resulting pressure is felt throughout the water. If we measure the hydrostatic pressure at any given depth, it is the same on all sides of the measuring instrument. While fluids do not resist shear, they do resist changes in the rate of change of shear.