For those of us who design and build stuff, reading well-documented and thorough accident investigations is immensely informative, and helps form better approaches to design, construction, and evaluation/test. Most aircraft and space accidents can fall under the heading of “complex systems fail in complex ways,” and failure is certainly an unforgiving teacher. I followed the Columbia investigation closely, and there were so many contributing factors; fixing almost any single one of them might have been enough to prevent the loss of spacecraft and lives. Commercial airline crash investigations from NTSB and BEA are also fascinating reading.