Nothing is a better teacher than failure or adversity.
The Challenger failure led to fundamental discoveries about the inadequacies of solid rocket motor joint design. Because that mission failure with loss of the crew was so devastating to the average American and members of Congress, numerous design and process reviews were held on all STS systems to uncover other potentially fatal flaws. My job, for many years, has been involved in the analysis of significant mission critical failures and the understanding of root causes for those failures. This complacency and the accompanying erosion of awareness of the consequences of failure leads to carelessness and a cumulative loss of reliability. The lights are usually on, the planes usually take off and land, the computers usually work, the launch vehicles and spacecraft usually perform marvelously, but no one pays attention until a system fails, then it's hell to pay.