To Enable a Design Authority to act upon User Experience, full and accurate information is required about the defect as soon as possible after it has occurred.

A skin crack in an aircraft structure, the loss of a turbine blade in a jet engine or excessively high brush wear in a generator, are all defects. The reasons for them being defects can be quite different in each case. One can therefore readily see that to solve these defects the designer needs to know not only everything about the failure, but also the environment (in the broadest possible sense) that led to the failure