When I went to business school, we talked about the Fraud triangle several times — at very least in my Ethics class and my Processes and Controls class.
Put simply, fraud doesn't happen without all three ingredients:
Motivation, or some kind of pressure to perform the fraud. It could be greed; it could be a genuine need to put food on the table.
Opportunity, both the capability to commit the fraud and being at the right time and place to see that you could do a fraud.
Rationalization, by being able to say why the fraud would actually be a good thing; getting back at a crappy company, helping yourself (motivation plays into this again), addressing apparent unfairness or injustice, or saying that it doesn't really hurt the victim because they have so much more money.
Most of the annoying stuff we have now to prevent fraud targets "Opportunity", but that's a moving target with more opportunities appearing all the time. As they say, "there's a sucker born every minute."
Which makes me wonder what could be done to improve the Motivation or Rationalization corners?