I have a two legged stool (by definition the legs are constrained perpendicular to the seat) where each leg is spherical ball jointed to a flexible floor.

I planned to stabilise the stool (constrain one leg perpendicular to the floor) by applying torsional stiffness (bushing) to one of the ball joints.

However no value of stiffness on any or all axes had any effect.  The stool kept falling over.

Which part of torsional stiffness do I not understand?