This is exactly what happens in the spiritual realm… God already gave, that is what spurs us to do good, and when we then do good, we are rewarded for it.
That is the core lesson of all mystic traditions , that at the beginning and at the end He is present, nothing escapes Him, neither the impulse nor the action, and both are His gifts, the first a blessing, the second a reward.
The mystic is she who does not break that circle, in the center of which she stands. Whether she is at the beginning of goodwill or at the end of goodwill, she is thankful, always, both for the inspiration and for the reward. In such a state, there is no fear, for fear fears to thread where appreciation roams :)
In the social realm, when we become aware in every interaction that we are deep into the gift-receiving, there is no other statement to make other than thank you, and this post does a fantastic job illustrating it.