Architecture & practice·Risk, blast radius and change
you could list what you did not know about the vendor's API, and that list was the plan.
Known unknowns
Also calledunknown unknowns
The risks you know you have not resolved yet, as distinct from the ones you cannot see at all. The useful move in planning is to make the first list explicit and attack it early with spikes, because a known unknown is schedulable and an unknown unknown is only survivable through slack. A plan that contains no known unknowns has not been examined, it has been asserted.