Everything being happiness thus indicates that all thoughts are the selection of a state of happiness matching their nature. Ergo, reality itself is a state of happiness since all perceptions of reality are only thoughts. Therefore, the only action you ever take is that of selecting a state of happiness and thus all actions are really just thoughts of a certain degree of happiness. Thus, with each thought you define the nature of your reality to be equal to the degree of happiness that is produced by the chosen thought.
By choosing a thought that produces the most desirable state of happiness, you thus make the state of your reality as desirable as possible. Furthermore, all desires are really just a desire for a specific state of happiness. The more alike in nature is the state of happiness produced by a thought to that which would be produced by the fulfillment of a desire, the closer you must be to its fulfillment.