To dwell upon the possibility of illness or disaster is equally poor policy, for you set up negative webs of probabilities that need not occur. You can theoretically alter your own past as YOU have known it, for time is no more something divorced from you than probabilities are. The past existed in multitudinous ways. You only experienced one probable past. By changing this past in your mind, now, in your present, you can change not only its nature but its effect, and not only upon yourself but upon others.