Henry was a person just like many of us, or at least seems like many of us in appearance. One unique single trait he had, that was known to everyone in town.
The day he was born, that was the day when doctors volunteer to dress up like clowns for altruistic purposes. One of the acting clowns was the doctor who received him, who held the baby high and through a face painted with extra-excited features exclaimed: - "Hello"- looking at henry straight in the eyes: -"Welcome to planet Earth! Remember to say hello, and thank you!".
The clown disappeared laughing, or henry was just overwhelmed by all the noises lights, voices. Henry was at that time only a few seconds old, he could only remember a couple of sounds and an image. Those sounds were "he-lo" and the image was first face he had ever seen.
Fast-forward a couple of decades, and while everybody else minded their own business on the street, Henry felt compelled to say "hello" to everyone. Additionally he had a preference for surprising people who were deeper in their own thoughts or lost in dreaming, because that way he could get the same expression he saw in the clown's painted face, over twenty years ago.
He does not realize what is really happening, why he behaves that way. Subconsciously is trying to evoke the same expression he saw in the painted face, that is why he tries to surprise everyone with a sudden Hello! He does not know that is a compulsive behavior, nor remember why he does it ...
--- the rest of the story may or not be in a book :)
~Book cover image was generated using Artificial Intelligence design wizard of DEFLAMEL