Reasons for errors can be considered to be like a block of Swiss cheese.
There are many holes in our defences but very rarely do the holes line up to create a clear passage through the cheese. In the same way, the contributing factors to error exist at all times within healthcare.
Some errors (the holes in the cheese) represent latent conditions; these are things that can go wrong in a system due to the way it is designed or managed. Examples are understaffing or inadequate equipment.
Other errors are due to active failures – unsafe acts committed by people who are in direct contact with the patient or system.
Latent failures can be identified and remedied by near miss reporting and risk management. Most incidents involve a combination of active and latent failures.
Reason JT. Human Error. Cambridge: Cambridge University Press; 1990.