Statistical thinking will one day be as necessary for efficient citizenship as the ability to read and write.

– H.G. Wells

When we speak of cost and schedule estimates, we must learn to speak of the statistical nature of the activity networks that produce those estimates. When we speak of a probabilistic activity network (a Bayesian network) we must learn to speak in terms of probability.

The first question asked of the network is – “ what is the probability of completing this task by a certain date?”

A second question asked is – “what are the underlying statistics of the activities of the network?”

A final question asked is “what is the inherent uncertainty in these estimates?” In other words – how good is our ability to guess in the presence of a statistical process?

If we don't learn to speak in these terms, we will be disappointed in the outcomes. Our managers will be disappointed in the outcomes. And we'll subject to Johanna's prophecy:

a serial life cycle provides a prediction that’s almost guaranteed to be wrong

and not even know why this is the case.