There are basically two ways of looking at ‘human error.’ The first view is known as the Old View, or The Bad Apple Theory. It maintains that:

Complex systems would be fine, were it not for the erratic behavior of some unreliable people (Bad Apples) in it.

‘Human errors’ cause accidents: more than two-thirds of them.

Failures come as unpleasant surprises. They are unexpected and do not belong in the system. Failures are introduced to the system through the inherent unreliability of people.