The Asymmetry of Burden

On the evening of January 27, 1986, Morton Thiokol engineers presented thirteen charts of O-ring erosion data to NASA managers and recommended against the Challenger launch. They were overruled—not by managers who dismissed the evidence, but by a process in which the structure of the argument made the recommendation extraordinarily difficult to sustain. The engineers wished to stop; the standard required them to prove that this specific launch under these specific conditions exceeded the limits the organization had already accepted. The party that wished to launch needed only point to the record of successful flights. The asymmetry was not a policy, not an instruction, not a conspiracy; it was a structural property of institutional life under production pressure that Diane Vaughan named and documented with forensic precision. The evidence for proceeding is always historical and concrete; the evidence for stopping is always predictive and speculative. The past has happened; the