trousergecko, it's a crude probability distribution, and the addition (i.e., discrete integration of the random variable with respect to the probability distribution function) represents the expected value of the outcome.
Have a read of http://en.wikipedia.org/wiki/Expected_value
It is for this reason that I am happy to hold at this price, but if it were to double, I would sell out (the risk is no longer better odds than the reward).