A lot of research has been done to determine why accidents happen, and how to prevent them from occuring. It's easy to blame an individual that may have done something wrong, but that's not usually the best way to solve a systematic problem.
British psychologist James Reason suggested in his Swiss Cheese model of accident causation that catastrophic safety failures are almost never caused by isolated errors committed by individuals. Instead, most accidents result from multiple, smaller errors in environments (the holes in the cheese) with serious underlying system flaws. In this model, errors made by individuals result in disastrous consequences. Reason also emphasized that human error is inevitable, and that a systems approach can catch errors before they occur or block them from causing harm.