The probable is what usually happens. —Aristotle

It is a truth very certain that when it is not in our power to determine. what is true we ought to follow what is most probable —Descartes, “Discourse on Method”

It is remarkable that a science which began with the consideration of games of chance should have become the most important object of human knowledge. —Pierre Simon Laplace - “Théorie Analytique des Probabilités, 1812

Anyone who considers arithmetic methods of producing random digits is, of course, in a state of sin. —John von Neumann - quote in “Conic Sections” by D. MacHale

I say unto you: a man must have chaos yet within him to be able to give birth to a dancing star: I say unto you: ye have chaos yet within you . . . —Friedrich Nietzsche - “Thus Spake Zarathustra”

Probability is about random variables. Instead of giving a precise definition, a random variable can be thought of as an uncertain, numerical quantity. While we do not know with certainty what value a random variable *X* will take, we usually know how to compute the probability that its value will be in some some subset of the population of values.

The collection of all such probabilities is the distribution of X. We need to be careful not to confuse the random variable itself and the distribution of random variables.

If we're going to make credible decisions using these random variables, we going to have to make estimates.

The estimates we create have precision and accuracy. These attributes should be defined *before* we start our estimating processes, so we'll then know when we have a *credible* estimate.

Estimating, Uncertainty, and Risk Management are inseparable processes. Each cannot deliver answers without the other two.

And always remember

Risk Management is How Adults Manage Projects - Tim Lister