It would be easier for you to fulfill your desires while feeling good rather than bad and thus you are making it easier for yourself to fulfill your desires by thinking thoughts that make you feel good. It would also be easier for you to fulfill your desires if you felt as you would were your desires already fulfilled rather than feeling drastically different feelings and since the thinking of thoughts about your desires already being fulfilled makes you feel good, the thinking of these thoughts will help you to fulfill your desires.
The Universe is vibrational in nature since you can feel the vibrations of the Universe by touching anything and your senses, feelings, could only arise as a result of your interacting with vibrations that differ from your own vibration, vibrations that alter the vibration of your body. Vibration is energy since energy, power, is derived from the vibration of one system, its energy level, acting on the vibration of another system and thus transferring its vibration, energy, to the receiving system.
Vibrations, energy levels, define the nature of systems such as thoughts and objects since your senses, your perception of vibrations, are derived by interpreting vibrations and thus vibrations define the nature of all perceived systems. The thinking of thoughts about your desires being fulfilled alters your vibration to match thereby changing who you are and that which you are experiencing and perceiving to also match the fulfillment of your desires.