Design mistakes

The source for many mishaps is that the designers enabled violation of the implicit rules. Typical design mistakes include:

Incomplete specifications, when the design boundaries are not defined, or when the specifications do not refer to all expected states
Poor specifications, when the documentation of the expected states do not represent properly the expectations of the stakeholders
Incomplete testing, when the plan does not include testing of unexpected events
Poor test plan, when the plan does not include testing of all exceptional situations, or all possible events
Invalid test plan, when the plan is to test according to the specifications, instead of the expectations of the stakeholders.