Infinite Intruder by Alan E. Nourse, Science Fiction, Fantasy

". . . .Every activity that makes an alteration, or has any broad effect on the future is a high-order variable, but many activities have no grave implications for future time, and could be considered unimportant, or low-order variables. If a man turns a corner and sees something that stimulates him into writing a world-shaking manifesto, the high-order variable would have started when he decided to turn the corner instead of going the other way. But if he took one way home instead of another, and nothing of importance occurred as a result of the decision, a low-order variable would be set up."