Product Acceptance Test (PAT) is a key event in the development of a system. It must be performed with great diligence, drilling down to the most detailed level of granularity relevant to the business, and with a tremendous amount of patience.

An 'easy' product acceptance will lead to errors found by the users during User Acceptance Test which will dampen the users' willingness to embrace the new product and might even lead to 'silent' rejection. Both situations are costly in business terms.