[2][3] The ETTO principle was originally proposed by the safety researcher Erik Hollnagel.
[1] The principle has been applied to analysis of behaviour and choices made regarding safety and risk.
There are competing activities requiring time, which is a limited resource.
In hindsight it is often obvious when and where such tradeoffs were made, and the consequences may be clearly linked to causes, but the trade-off seemed like a good idea at the time, and for as long as things kept going right.
[4] The principle of requiring "reasonably practicable" precautions in occupational health and safety recognises that such trade-offs must exist to allow economic activity to proceed, and puts the onus on the employer to assess the risk and take those precautions.