To put it in a nutshell, several thousand years ago some bad apples among us didn't play by the rules. They got carried away and caused a lot of trouble, and they didn't fix things up when they were finished. That's when somebody got the bright idea of carving the words shih kan tang on a stone tablet and setting it up in the neighborhood.
簡言之，在幾千年前，吾輩中有些不肖者，不依規矩行事，做的太過火而惹上麻煩，事後調解不成，有人在石上刻銘「石敢當，鎮百鬼，厭災殃，官吏福，百姓康，風報盛，禮樂張。」