From Tullock‘s chapter on “Becoming a Dictator” in Autocracy:

Economists know the so-called random walk hypothesis regarding the stock market, which holds that all available information is already incorporated in the market price, with the result that the price or its recent movements have no predictive value.  Something vaguely like this is important in [dictatorial successions].  The dictator probably knows as much as anybody else does about his immediate inferiors.  Thus, if one of them appears to be in a position where he might be able to overthrow the dictator, this probably indicates that the dictator is about to get rid of him.