Or the unit of measure. It's really hard to tell what sort of technical debt you are taking on and building for contingencies that may never manifest is it's ow

Or the unit of measure. It's really hard to tell what sort of technical debt you are taking on and building for contingencies that may never manifest is it's own type of sunk cost. That's (a) why projects need to have some strategies that move forward without excluding lateral (or minor-backtracking) moves, and (b) why software development is inherently hard.