We often think of human errors as one-off, discrete, undesired events.  However, the reality is that error is a natural and integral part of human behaviour.  Let's face it, a lack of precision and the ability to adapt and work flexibility is what makes people human.  Therefore, the analogies of human error being a weak link in a chain of events or the very notion that we can prevent errors does not stack up. 

The well known 'fire triangle' shows us that fire occurs because three elements are present that, if you are lucky or unlucky (depending whether you want a fire or not.