Vince Gilligan is the creator of Walter White, the biology teacher turned meth chef in Breaking Bad. Here are his interesting thoughts about how he set about characterizing this man and charting the way he changed into a sociopath. I found his discussion of the teddy bear in the pool intriguing-- he started with the image, understood it was a sign from the subconscious, and realized he'd have to figure out where the teddy bear came from. (This is, btw, the same way the event is presented in the episode-- that is, our own experience replicates the creation of the plot thread.)
Has that ever happened to you, when you get an image or idea or snatch of dialogue and have to create a storyline to explain it?