We plan out our jobs, workflow, schedules … everything we can think of. And then we try to factor in the unexpected with contingency clauses and other exclusions.
But there is a rub. Once we factor in a specific potential problem, it is no longer unexpected. We have anticipated it and allowed for the possibility that it might occur. So it now becomes expected.
The collective volume of these expected events is called experience, which could be defined as having been around long enough to make most of the common mistakes.
The unexpected is still out there. For everything we have learned, there are any number of things we still have to learn. If these events were expected, we would already be aware of them and safe from being blindsided.
I would suggest that it is impossible to factor in the unexpected other than to be aware that it is out there, ready to teach us yet another lesson.