Quality at the source is the principle that errors should be detected and stopped where they arise — by the process and the employee that create them — instead of being caught by inspection further down the chain. No defect is passed on.
The further an error travels, the more expensive it becomes: an error caught at the source costs minutes; the same error at the customer costs a complaint, freight, rework and trust. Final inspection is the most expensive and least reliable quality strategy.
The means are self-inspection with clear standards, poka-yoke, andon and a culture where it is welcome to stop and say an error out loud — the last is the hardest.