James Reason, The scholar of catastrophe who uses Nick Leeson and Barings Bank as a case study to help engineers prevent accidents, is careful to distinguish between three different types of error. The most straightforward are slips, when through clumsiness or lack of attention you do something you simply didn’t mean to do. In 2005, a young Japanese trader tried to sell one share at a price of ¥600,000 and instead sold 600,000 shares at the bargain price of ¥1. Traders call these slips ‘fat finger errors’ and this one cost £200 million.
Then there are violations, which involve someone deliberately doing the wrong thing. Bewildering accounting tricks like those employed at Enron, or the cruder fraud of Bernard Madoff, are violations, and the incentives for them are much greater in finance than in industry.
Most insidious are mistakes. Mistakes are things you do on purpose, but with unintended consequences, because your mental model of the world is wrong. When the supervisors at Piper Alpha switched on a dismantled pump, they made a mistake in this sense. Switching on the pump was what they intended, and they followed all the correct procedures. The problem was that their assumption about the pump, which was that it was all in one piece, was mistaken.