It's good to give someone a gift as a reward.
Bill returns from a week long vacation during which time his friend Greg was dog sitting for him.
Bill wants to thank Greg for helping him out.
Bill thanks Greg in person and gives him a substantial gift certificate as a reward for dog sitting.
Bill leaves Greg a short voicemail telling him thank you for dog sitting.
Greg is happy, appreciative and eager to help dog sit again in the future.
Greg feels underwhelmed and a bit unappreciated by Bill's response and declines to dog sit for him in the future.