Here's why:

* Viscosity refers to the internal friction within a fluid. It's a measure of the fluid's resistance to flow.

* Uneven forces acting on the surface of a liquid can cause surface tension. Surface tension is a different phenomenon that arises from the cohesive forces between liquid molecules at the surface.

In summary:

* Viscosity is about internal friction within a fluid.

* Surface tension is about forces acting on the surface of a liquid.