The Deepwater Horizon rig was 43 days behind schedule and costing $1m a day. To save time on the final cementing of the well, operators ran a shorter test, used fewer centralisers, skipped a positive pressure test. The well blew out on 20 April 2010. Eleven workers killed; 4.9 million barrels of oil into the Gulf of Mexico.
The principle: Each individual corner cut is too small to alarm anyone in isolation. The disaster is in the stack: six small compromises individually fine, jointly catastrophic. The pressure that caused each compromise is the same pressure that prevents the team from auditing the stack.