Mistake proofing is an effort to stop defects at the source. The prime objective is to prevent defects from occurring in the first place, but if they do occur, to stop their progression through the process. By stopping a defect at its source, its cost impact is minimized.
The further the defect progresses through a process, the more waste occurs. The more waste that occurs, the higher the cost impact. As a result, the best place to stop a defect is in the design of the process, product, or service. Once the process is in place, waste starts to be generated as a process output along with the product or service.