Decision making in complex environments
The environment within which people make decisions is complex with overlapping components including other people, things, goals, rules, values, knowledge etc., which are in turn complex sub-systems. Decisions are made with the limited information available to the decision maker at the time, within local contexts and based on knowledge of what makes sense at the local level. This is the principle of local rationality - decisions are rational to the decision maker because they are based on the information available within the local context and at a particular point in time.
The factors that are most obvious, pressing and significant from one person's point of view aren't necessarily obvious, pressing or significant from another person's point of view.
People do things that make sense to them, given their goals, understanding of the situation and focus of attention at that time
Analysis of decision making
When investigating unsafe behaviour, decisions taken by a pilot or air traffic controller may not seem rational. Why were rules broken? Why were procedures not followed? Why was a particular course of action chosen? Why did someone deliberately cut corners? A starting point in any analysis should be to accept that the decision made sense to the decision maker at the time, and then seek to understand the local rationality - why was the decision "locally rational"? There may be numerous factors and combinations of factors.
If you find out which factors are at play in a decision before you try to change a person's behaviour, then you will be much more successful at creating sustained change.