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When performing functional safety hazard assessments, the challenge is anticipating all the things that can go wrong during a system’s operation. Hazard assessment tends to be performed in an ad hoc (where do I begin assessing?) and open-ended (when do I stop assessing?) manner. It is difficult for humans to factor in all the variables that affect a system’s nominal interaction with the environment and then predict all the combinational behaviors (good or bad) resulting from those variables. Quite often, after the system is built, a hazardous situation will occur that no one expected, and perhaps even assumed improbable. At those times engineers may employ a postmortem and realize that, with enough forethought, the hazard could have been assessed and anticipated. In contrast to the postmortem, there is the premortem, which tries to assess what can go wrong, before it actually occurs.