The term error must be dispensed. In this chapter you will get a working definition that will work as a framework.

Errors are not fundamentally bad. It is often the case that the circumstances of their occurrence shape the consequences of the error. For example, switching on the light in the kitchen instead of the light in the hallway will not have very bad consequences, but switching on the wrong switch when you’re flying an airplane can be disastrous. Reason also proposes that all human actions have three basic elements: plans, actions and consequences. Each of the elements will be explained below.

Plans

Plans are central to our understanding of errors. All humans plan, you probably know what you are going to do today, tomorrow, next week and maybe even next year. The more long-term your plans are, the more vague they get.

Keep this example in mind while we discover what planning entails: You are hungry, it has been a hard morning and you want to treat yourself. You consider different cuisines but decide on Italian, because you are feeling a unique pizza for lunch. Do you want to go to the Napoli or the Italia? You decide that the Napoli is easier to reach with the bus. The only problem is now that you are on a diet and that pizza is not low in calories.

The plan (having lunch somewhere) starts with a need to alleviate a state of tension (hungry and feelings about the hard morning). After the need there is the intention (having a lunch to treat yourself). This intention turns into a goal that can be achieved with different means. Having made a particular plan (having lunch at Napoli), you only have to assemble and specify the action sequences (how do you get to Napoli).

Can a planner help?

A planner does not have to plan every detail of an action; because a lot of what we do already has different mental and verbal tags that lead to largely automatic subroutines. The more we engage in these habitual actions, the less tags we need to specify our planning.

When you arrive safely at the Napoli and had a delicious pizza, what was the error in the plan? Well, you clearly did not hold you to your dietary plans, which was a long-term plan of yours. Because we make so many plans that interact with each other, it is hard to pinpoint the point where we make errors. In general there are two types of plans: co-existing plans and conflicting plans (the pizza lunch and the diet).

There are two built-in-limitations to human performance. The first is that we can’t always have the physical capacity to turn a personal plan into action; we just can’t be at two places at the same time. Secondly, we don’t have enough mental capacity to carry out all our plans.

For the purpose of this book an error is defined as: “The term error will be applied to all those occasions in which a planned sequence of mental or physical activities fails to achieve its desired goal without the intervention of some chance agency”. The two important things to remember from this definition is the notion of intention and the absence of a chance intervention.

There are two ways in which you can fail to achieve your desired objective:

• Failures, such as slips and lapses (absent-mindedness) or trips and fumbles (clumsy or maladroit actions) occur at the level of executions. There is nothing wrong with the plan of action.
• Failures that arise from the plan itself, this involves mistakes and are much more complex and harder to notice.