Every conspiracy theory starts as a notion nestled safely in someone's head, just waiting for a chance to spread. Some are harmless fun (Keanu Reeves is immortal), while others are deadly (vaccines cause autism). But all run on the same psychological tricks: They make believers feel more in control of a chaotic world. Folks cling to stories that affirm their beliefs, explain away mysteries, and provide scapegoats for their troubles. But there are many paths to infamy. Which will you choose?