•You may not know it, but every atom/molecule in your body is
oscillating.
•For any system, there's at least one state that the system is
of the lowest potential energy. This is a point of stable equilibrium, or the bottom of the
valley in a potential vs. position curve.
•If the system is of a small displacement from the point, it'll
experience a restoring force, pointing
to the bottom of the potential curve.
The force accelerates the system so it'll swing across the equilibrium point to the other side, and the
restoring force will reverse as well. Thus, it'll oscillate
around the point of equilibrium.