Despite having handled nearly 500 workplace fatalities, I once found myself hanging three stories from a gutter because I had wedged a piece of firewood under my ladder rather than taking five minutes to properly set it. Why does a skilled person with awareness of the dangers of cutting corners nonetheless take unnecessary risks?
"Nonchalance" is a greater hazard than a lack of training or experience. Seventy percent of the workplace fatalities I have handled were due to errors by well-trained employees. Some were driven by the desire to take care of the job as swiftly as possible. Others figured that they had successfully "done it before." Others apparently just didn't think.
Unsafe attitudes develop "incrementally." J. A. Rodriquez has explained how employees engage in "incremental rationalization" whereby they bit-by-bit justify ultimately disastrous final decisions. Rodriguez analogizes to our well-known incremental justification for violating our diet plans, in which the rationalization proceeds from "I know I shouldn't have it" to "maybe just this once" to "I deserve this," and so forth.