Rhythm states that everything swings, and then adds a second claim that is easy to read past: the swing to the right is measured by the swing to the left. The Kybalion calls this the Law of Compensation and treats it as the reason a run of good fortune is paid for later, and the reason a depth of grief is the price of a height of love.
Attached to it is the only genuinely technical instruction among the seven. The book describes a mental art it calls neutralisation, which consists of refusing to be carried by the backswing by holding a position above the plane on which the swing is happening. The practitioner polarises at the desired pole and then declines to move. It is close kin to the detachment taught in Stoic and in Buddhist practice, although the book claims no such ancestry and names no such source.
Where the principle overreaches is in insisting that the compensation is exact. Nothing in the text supports that beyond assertion, and the same claim in a stronger form is what makes popular readings of karma objectionable to their critics, because it implies that suffering has been earned. Read narrowly, as the observation that moods and fortunes oscillate and that the top of a swing is a poor place from which to make decisions, Rhythm is the least contentious of the seven and the easiest to test against a life.