What is the story behind PostSecret?

My first day in Paris I had purchased three Antoine de Saint-Expery's "Little Prince" postcards from a small shop near my hotel. When I got to my hotel room and prepared for bed I placed the cards in the nightstand drawer and went to sleep. During the night, I had a lucid dream in which I was aware that I was in my own dream. I found myself in my hotel room. In my dream I opened my nightstand drawer and examined the three "Little Prince" postcards.

 Each one had been altered with messages written on their backs. The first message read, "unrecognized evidence, from forgotten journeys, unknowingly rediscovered," the second message was about a "reluctant oracle" postcard art project and the last message I could not understand at the time.

(...)

 The last message from "reluctant oracle" bore the message, "You will find your answers in the secrets of strangers." The next Sunday the PostSecret began.

What is the story behind PostSecret? | PostSecret Community