Only fools and the bankers who created the GFC think the future is absolutely predictable. The rest of know there is always a degree of uncertainty in any prediction about what may happen at some point in the future. The key question is either what degree of uncertainty, or in project management space what is the probability of achieving a predetermined time or cost commitment.

There are essentially three ways to deal with this uncertainty:

Option oneis to hope the project will turn out OK. Unfortunately hope is not an effective strategy.