Better wrong than vague

An articulated guess beats an unspoken assumption

Frederick Brooks

A point that Fred Brooks makes in his recent work the Design of Design is that it’s wiser to explicitly make specific assumptions, even if that entails guessing the values, rather than leave the assumption un-stated and vague because ‘we just don’t know’. Brooks notes that while specific and explicit assumptions may be questioned, implicit and vague ones definitely won’t be. If a critical aspect of your design rests upon such fuzzy unarticulated assumptions, then the results can be dire.

Brooks also makes the case that the apparent extra effort of surfacing such issues is in fact illusory as all designs are be based on a raft of assumptions, the choice is simply whether one makes them explicitly or not. I also think that the degree to which assumptions are documented is a telling measure of the quality of a design, one that is also rarely used. A question for me is how to characterise the risk posed by un-stated implicit assumptions, my current thinking is that they fall into the fourth risk quadrant as “unknown, unknown’s” or ontological risk, as the European Space Agency found to it’s cost on the Ariane 501 mission.