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Poka -yoke or Mistake Proofing is about using a process or design feature and control mechanisms to prevent defects, detect them if there are not preventable. reduce the severity of the defects. The main motive is to: PREVENT a defect from occurring and if that is not possible, DETECT the defect every time it occurs. It is critical to prevent and detect errors/ defects as early as possible in the process because the later they are found the more expensive they become i.e. costs associated with them increases - more materials, labour, overhead, time. While implementing poka-yoke designs, care should also be taken that the implementation does not enhance any other issues or open new issues that may cause defects. Poka -yoke or Mistake Proofing has varying degrees of effectiveness. - Control Vs Warning Poka yoke. One must balance getting the most effective poka-yoke while keeping in mind the practical and economic feasibility of the solution. I feel all the interpretations provided in the question are all correct and validate the varying degrees of effectiveness. 1. The human error will not happen at all. Example: Rectangular design of 3.5” floppy disc so that the wrong side cannot be inserted. SIM card slot in cell phones is designed in such a way that user can insert SIM card in correct way only. There is no chance for user to make a mistake while putting SIM card in a cell phone or floppy in the drive. 2. Human error may continue to happen but the defect will not happen. Example: Validation check when creating new password to contain the required combination of Upper, lower case, numeric and special characters to ensure a strong password. The system does not accept a password unless it fulfils the criterion. Double Entry Box: Most websites & software where one needs to enter a critical bank account number, or a password create option, users are asked to enter the same value twice (with paste option disabled). This is to ensure people haven't made a mistake while entering the value, and that both boxes hold the same value 3. Human error may happen, the defect is less likely to happen. Example: Some of the email software pop up an error message like “there is no attachment, do you want to send it anyway?”, if they find the key words “Find attached” (or other variants of the same) and do not see an attachment when the user tries to send the email. Some Email software pop up a message if the subject is missing when the user tries to send the message. Car Seat belt Warning indicator beeps to warn that the user has forgotten to put on the seat belt, if he drives without putting on the belt. 4. Human error may happen, the defect will also happen but will be detected and corrected automatically. Example: Microsoft word, Google search automatically corrects typographical spelling error. Auto logout functionality in websites (especially Banks). When user forgets to logout before closing the website and reopens, then he has to provide the credentials and log back in.