"A plot, I used to remind my students, is not merely a sequence of events: "A" followed by "B" followed by "C" followed by "D." Rather, it's a series of events linked by cause and effect: "A" causes "B," which causes "C," and so on. True, a person's (or a fictional character's) destiny may be more than the sum of his choices--fate and luck play a role as well--but only scientists (and not all of them) believe that free will is a sham. People in life--and therefore in fiction--must choose, and their choices must have meaningful consequences. Otherwise, there's no story."