Yeah, lib arts types can't understand risk assessment. But what he said is quite true; it just sounds dumb on the surface.
Every project should account for those unknown unknowns.
It's kinda line when I write a 12 page letter to a client evaluating, in painstaking detail, every nuance of a complex case that is going to trial, including an analysis of the anticipated outcome based upon research about historical cases and my own experience...then I end the letter by saying: "...but you never know what a jury will do, so anything is possible."