A 2-step technique for assuring functionality of (business) processes

Coming from the world of theatre I use this basic mechanism to ensure safety and usability for stage and stage effects that translates easily into a technique for business processes.

For example, to ensure that a spotlight attached to a traverse does not fall down, you should use an additional safety: Brackets hold the spotlights and for the unpredictable case that a bracket fails, an arresting cable is attached additionally. The cable has to go over the rod or through the bar without any possibility to slide off sideways (end delimiters). This is pursuant to insurance law for theaters, but may be applied to processes in an office, too.

For example, you may have a filing with cards in your private library or a tray where customers´ letters are deposited for some handling in the future. Let´s say you need further information from the customer before you can proceed. As time goes by, more and more letters will pile up.
And if you are working professionally, i.e. responsibly, you may establish a weekly process where the pile gets reviewed regularly. In that way you may check that for every customers´ letter or every borrowed book action has been taken in time.

Where are we? What are the odds now?

Let´s say that staff members forget to contact customers or forget to file them in your electronic database with p=0.01, i.e. every 100th customer. In general this won´t surface as you may assume that at least p=0.66 customers will call back if they do not receive payment or other information in time. So on average you may have only a slight problem in 1 of 300 cases.
But if you use your weekly process with an estimated error probability of 0,001, conditions change dramatically. Within two weeks you may expect only one error in 300.000.000 – which is far beyond the chance for winning the German lottery.