Suppose that you filled a baking dish to the rim with water and walked around an oval track making an attempt to complete a lap in the least amount of time. The water would have a tendency to spill from the container during specific locations on the track. In general the water spilled when:
the container was at rest and you attempted to move it
the container was in motion and you attempted to stop it
the container was moving in one direction and you attempted to change its direction.