The graphic from explains the concept of the Swiss – Cheese – Model very catchy. The model describes that it is better if we provide different protection systems. The idea is that all systems will (have to) have holes in them, but since all systems are superimposed on each other, the chance of something happening is very small.

Despite all our best intentions accidents happen. The analysis of accidents and incidents in large complex systems such as power plants or plane crashes led to the conclusion that “no human or technical failure is sufficient to cause an accident. Rather, it is the unlikely and often unpredictable interaction of several contributing factors occurring at different levels of the system”.

The model is a nice reminder that several layers of defense are more effective but that something is going wrong. Perhaps it might also help if we look again at the main reasons for failure: 

  • Human error will always exist, it is inevitable: Human error is not a moral issue. Human fallibility can be tempered, but it can never be eliminated.
  • Mistakes are not bad: success and failure have the same psychological roots. Without them, we could neither learn nor acquire the skills that are essential for safe and efficient work.
  • Mistakes are the result, not the cause: … mistakes have a history. The discovery of an error is the beginning of a search for causes, not the end. Only when we understand the circumstances … can we hope to limit the chances of repetition.
  • Many mistakes are made over and over again: the most effective way to use limited resources for error management is to target these recurring types of errors.
  • Safety-relevant errors can occur at all levels of the system: Making mistakes is not the monopoly of those who get their hands dirty. …the higher a person is in an organization, the more dangerous their mistakes are. Error management techniques must be applied throughout the system.
  • Effective error management aims at continuous reform rather than local correction: There is always a strong temptation to focus on the last few mistakes … but trying to prevent individual mistakes is like beating mosquitoes … the only way to solve the mosquito problem is to drain the swamps in which they breed. Reforming the system as a whole must be a continuous process, the aim of which is to contain whole groups of errors rather than individual errors.
  • People cannot easily evade actions that they did not intend to commit: Blaming people for their mistakes is emotionally satisfying, but there is no point in correcting them. However, we should not confuse guilt with responsibility. Everyone should be held accountable for their mistakes [and] acknowledge the mistakes and try to be careful to avoid repetition.

Here is an excerpt from Revisiting the “Swiss Cheese” Model of Accidents by Reason, Hollnagel and Paries from 2006 for people who would like to know more.