If you are familiar with the Law of attraction, you may be aware of three steps that are required for successful manifestation. 1) acknowledging desire 2) calling for desire 3) allowing desire to manifest.
Most of the people fail during the step 3, because of negative spectrum of frequencies that defy getting into the state of allowing and receiving. Since like attracts like, we can not attract, or receive positive spectrum of desires while being in the state of lower vibratory fields.
So the gratitude, is like a shortcut to transcend from lower into higher frequencies, energies, emotions, feelings, fields where manifestations occur effortlessly.
We all say "thank you" many times during the day, however not all of us understand the power of this simple expression. Emotional signature of gratitude, has transcending qualities that can be utilized to refocus the attention in positive direction.
There is another beautiful expression "from the bottom of heart" or else, "with full heart" which means sincerity, the truth of the matter.
Similarly, if we combine the power of heart while expressing gratitude, for the desired events as if they have happened, without expectations, but rather knowing, we unlock the potential of the simple "thank you".