ETTO principle

Erik Hollnagel

Ph.D., Professor, Professor Emeritus


The ETTO Principle - Efficiency-Thoroughness Trade-Off


ETTOing well is the pathway to glory;

ETTOing badly will make you feel sorry!

It is a fundamental characteristic of human performance, whether individual or collective, that the resources needed to do something often, if not always, are too few. The most frequent shortcoming is a lack of time, but other resources such as information, materials, tools, energy, and manpower may also be in short supply. We nevertheless usually manage to meet the requirements to acceptable performance by adjusting how we do things to meet the demands and the current conditions - or in other words to balance demands and resources. This ability to adjust performance to match the conditions can be described as a trade-off between efficiency and thoroughness.1 The essence of this balance or trade-off between efficiency and thoroughness is described by the ETTO principle, which, in its simplest possible form, can be stated as follows: In their daily activities, at work or at leisure, people (and organisations) routinely make a choice between being effective and being thorough, since it rarely is possible to be both at the same time. If demands to productivity or performance are high, thoroughness is reduced until the productivity goals are met. If demands to safety are high, efficiency is reduced until the safety goals are met.

A formal definition

The ETTO principle refers to the fact that people (and organisations) as part of their activities frequently – or always – have to make a trade-off between the resources (primarily time and effort) they spend on preparing to do something and the resources (primarily time and effort) they spend on doing it. The trade-off may favour thoroughness over efficiency if safety and quality are the dominant concerns, and efficiency over thoroughness if throughput and output are the dominant concerns. It follows from the ETTO principle that it is never possible to maximise efficiency and thoroughness at the same time. Nor can an activity expect to succeed, if there is not a minimum of either.

  • Efficiency means that the level of investment or amount of resources used or needed to achieve a stated goal or objective are kept as low as possible. The resources may be expressed in terms of time, materials, money, psychological effort (workload), physical effort (fatigue), manpower (number of people), etc. The appropriate level or amount is determined by the subjective evaluation of what is sufficient to achieve the goal, i.e., good enough to be acceptable by whatever stop rule is applied as well as by external requirements and demands. For individuals, the decision about how much effort to spend is usually not conscious, but rather a result of habit, social norms, and established practice. For organisations, it is more likely to be the result of a direct consideration – although this choice in itself will also be subject to the ETTO principle.
  • Thoroughness means that an activity is carried out only if the individual or organisation is confident that the necessary and sufficient conditions for it exist so that the activity will achieve its objective and not create any unwanted side-effects. These conditions comprise time, information, materials, energy, competence, tools, etc. More formally, thoroughness means that the pre-conditions for an activity are in place, that the execution conditions can be ensured, and that the outcome(s) will be the intended one(s).

The ETTO fallacy is that people are required to be both efficient and thorough at the same time – or rather to be thorough when with hindsight it was wrong to be efficient!

(1) Simplifying the characterisation of human performance to a trade-off between efficiency and thoroughness is, of course, itself an example of such a trade-off.