The ETTO Principle


Professor Erik Hollnagel (PhD, psychology) would prefer to be able to explain why – for most of the time – we do things right, and to use this knowledge to shift accident prevention thinking from identifying causes to understanding and supporting human creativity, learning and performance variability. Resilience Engineering proposes a simple principle which can be applied to any situation or domain to reveal the “trade-offs” we make in the pursuit of attaining our goals: the Efficiency/Thoroughness Trade-Off (ETTO) principle. We make these trade-offs for a variety of reasons in order to get something done: on the side of thoroughness, we pay more attention to safety; on the side of efficiency, we do things faster. These trade-offs are not made for any bad reason, but for the greater good.

In an example taken from nature, Hollnagel argued that birds display ETTO every day when they risk eating in the open, where food is plentiful and the danger is greatest, as opposed to eating less but in safety. Indeed, human ability to adjust performance to changing circumstances is also a key to our success. Things go right most of the time, but occasionally and inevitably, an unforeseen combination of the same trade-offs result in accidents. The origin of both success and failure is the same: performance.

Source: To Err Is Human: The ETTO Principle