Let's compare this distribution process to an elevator in a five-story building. Think of the first floor as ground state and the fifth floor as excited state. When energy is applied, the elevator goes straight to the fifth floor, where its passenger (electron) gets off. However, the fifth floor is too small and unstable for many to stay for long periods of time, so most electrons go down to the fourth floor. The fourth floor is the "metastable state." Electrons can stay longer on the forth floor than on the fifth floor, but most return to the first floor (ground state), emitting energy. As you can see in the diagram below, we end up with a distribution in which most electrons are on the first floor (ground state) while only a few are on the fourth floor (metastable state).