Generally without recognition, every person's life is daily affected by a series of “probability models” that profoundly affect his or her future. Without any form of interference, the “crude” probability of breaking a leg during a single day might be 50%. This crude probability is reduced, perhaps 100-fold, by opening the eyes and watching the floor while walking about; this latter probability is further diminished, say 10-fold, by removing any children's toys strewn over the floor and stairs. The probability—already reduced to 0.05%—can be significantly improved (probably by 4 orders of magnitude) by checking for traffic before crossing the road and by caution while standing at the edge of the station platform. The risk of breaking a leg—now reaching a more acceptable level (0.000005%)—continues to be affected by largely unalterable short-term fluctuations (injury by a rogue motorist or a remote chance of building collapse) or longer-term fluctuations, such as critical weakening of a long bone by osteoporosis or the presence of a metastasis.
Rose GE. A Personal ViewProbability in Medicine, Levels of (Un)Certainty, and the Diagnosis of Orbital Disease (With Particular Reference to Orbital “Pseudotumor”). Arch Ophthalmol. 2007;125(12):1711-1712. doi:10.1001/archopht.125.12.1711