“Everything flows out and in; everything has its tides; all things rise and fall; the pendulum-swing manifests in everything; the measure of the swing to the right is the measure of the swing to the left; rhythm compensates.”- The Kybalion
The Principle of Rhythm states that all things have a measured motion. That is, with all vibration comes its opposite vibration which assists with the vitality of that vibration. Everything swings between these two poles in a measured motion, and thus you have rhythm.
Think about the seasons and the weather that accompanies each season. Each season is necessary for the balance of the environment- extremes in either direction would be disastrous; a winter that never ends (we’re not in Westeros folks), a summer that goes on and on… frankly this would also mean that Earth has stopped spinning, and life as we know it would cease to exist… so yes, the balance, the moderation of the measured motion, is essential!
Rhythm manifests in other ways as well. A person who feels joy intensely often also feels sadness intensely. Conversely, a person who feels little joy in anything also tends to little sadness. The measure of the swing to the right is the measure of the swing to the left.
The pendulum swings into high vibratory planes and then into low vibratory planes and back again. A period of intense happiness can be followed a by a period of intense sadness. A period of depression is followed by a period of happiness. However, it does not always have to be this way. A person who understands the Hermetic Principles can use the Law of Neutralization to eliminate the swing to the lower vibratory plane. Using mental transmutation you can keep your vibration high and thus escape the effects you would endure as the pendulum swings back to the lower vibration.