A popular motto is 'Failure is not an option'. The problem is that with humans failure is inevitable. If there is some way of screwing it up, given enough people and time, someone will screw it up.

The keys are to design systems that are resistant to common human failings of inattention and sloppiness, and to build in safeguards so that no single failure, or even a few, causes a huge loss. Humans get complacent, bored, and sloppy. After the first few hundred time carefully checking, and not finding any hazard, it is easy to assume the risk is more theoretical than real. Safety procedures stop being a habit. People get hurt.

A good example is a procedure BellSouth used to use. They made it policy that drivers would place a safety cone behind the service truck after parking. They made it a potential firing offense to not do so. A lot of employees were outraged at being forced to do something so inane. I mean, exactly what good would a plastic cone do?

As it turned out it was an effective safety technique. The cone helps keep people from parking too close to the rear of the truck. But the big payoff was that having to walk behind the truck to retrieve the cone forced people to observe what was behind the truck immediately before backing out. In effect it forced them to check their blind spots. The number of accidents involving people backing into people and things dropped. The company saved money.