Sunk costs are defined as costs that have already been incurred and cannot be recovered. Proponents of the sunk cost fallacy argue that since it is a cost paid in the past and unrecoverable, it should be removed from any future decision making.
The cost of quality isn’t discussed much. More often, the cost of poor quality hogs the limelight and the headlines. Cost of poor quality costs are believed to be 100% avoidable, and thus are assigned resources to expend extra attention and efforts to eliminate.