The founder of Reiki, Dr Mikao Usui created the five principles of the Usui Natural Healing System called Reiki. He recognised an individual's appreciation and gratitude in his ability with healing. From my perspective it is not just the practitioner that must feel grateful the client must feel grateful, clients who seek healing must also play an active role in the healing process. To change a situation in one's life there must also be a change in attitude - as what one thinks is what shall be.
It is based on this theory - projecting only thoughts of love and thankfulness is to create a life full of love and abundance.
Here are the five spiritual principles:
It is generally believed among Reiki practitioners that living by these principles they will place themselves in the flow of life - what you think is truly what you are.
These principals are basic tenets of good living. It means that one is kind, compassionate, tolerant and accepting of others and their behaviours. Positive thinking creates positive energy.

Cheers
Have a happy day.