Right and it's specifically for action that we need to know the odds. To pick one set of actions in advance of an uncertain event we need to know three things:

Right and it's specifically for action that we need to know the odds. To pick one set of actions in advance of an uncertain event we need to know three things: - The cost in case the event turns out bad, - The upside in case the event turns out good, and - The probability that the event turns out good. We can summarise the two first ones as "the payoff function of the event" and simplify the situation into requiring knowledge about the payoff and the probability. But without the probability we cannot take informed action. (Unless the payoff is structured such that the probability doesn't matter -- but then it's also not much of a difficult decision.)