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Chapter Six. The Holes in the Cheese. How Safe Systems Fail Anyway Disasters are never caused by one thing. They happen when multiple layers of protection quietly erode until the moment they're needed most and aren't there. On the night of January 27, 1986, a group of engineers at Morton Thiokol sat around a conference table and tried to stop a launch. Roger Boisjoly was one of them. He had been raising concerns about the solid rocket booster O-rings for months... the rubber seals that held