A deal that only works when everyone behaves perfectly is poorly negotiated.

Any arrangement that only holds if nobody gets sick, delayed, distracted, or difficult is not really an arrangement. Real conditions include failure, and terms that assume otherwise simply push the problem forward to a moment when the goodwill has run out. Building for imperfection is what separates a durable deal from an optimistic one.

Walk through the arrangement assuming both sides perform at eighty percent. Ask what breaks and write down what happens then. It is a short exercise and it catches most of the trouble.