  Gott has promulgated a rule for making probabilistic predictions of the
future duration of a phenomenon based on the phenomenon's present age [Nature,
Vol. 363, 315 (1993)]. I show that the two usual methods for deriving Gott's
rule are flawed. Nothing licenses indiscriminate use of Gott's rule as a
predictor of future duration. It should only be used when the phenomenon in
question has no identifiable time scales.
