But I don't think the point of this is to look at it from the investors' point of view. The point is to look at it from the founders' point of view. That is, as a founder, what's your basic (binary) chance of your company being a success? Founders don't get the chance to diversify across many companies - all of their eggs are in one (their own company's) basket. Thus, for them, a "percentage chance of a positive outcome" is an important metric.