The Challenger disaster investigation made an uncommon theory quite suddenly very famous amongst investigators.
“Normalisation of Deviance”

Described by Columbia professor, Diane Vaughan, “Social normalisation of deviance means that people within the organisation become so much accustomed to a deviant behaviour that they don’t consider it as deviant, despite the fact that they far exceed their own rules for the elementary safety”

Explained differently. Imagine there is a road on your way to work that you always go a little bit faster than the speed limit. You never get caught, so every day you continue to exceed the speed limit on this bit of road, sometimes going dangerously fast. This is deviant behaviour. Your safety is at risk but your risk assessments every day allow you to think it’s ok. Until one day the conditions aren’t ideal, you skid off the road and cause a terrible accident. Normalisation of Deviance.

The engineers that built the solid rocket boosters for the Space Shuttle also knew there was a problem with their design. A primary O-ring sealing rocket fuel has had previous faults. The engineers all know about the fault. They continue to assess the risk of failure as low. On the day of Challenger launch the conditions aren’t ideal. Cold, icy weather hardens the o-ring, making it brittle. During launch it fails, causes a leak in the SRB and explodes, destroying the entire Space Shuttle and kills 7 astronauts. Normalisation of Deviance.

History has shown us many examples of this behaviour.
Titanic
Costa Concordia
The Bedford Gulfstream crash (this ones a ripper. Google it)

If you are involved in known deviant procedures or behaviour, put your hand up, you may be the one to save the day.