Bruce Schneier is a widely recognized expert on security, with a specific emphasis on computer security. He wrote an essay on scams a bit over a decade ago. While things have changed a lot since then, it is still an interesting read from the perspective of the scammer attacking the human behind the keyboard with ideas, rather than trying to write a virus to infect the computer.
A much more recent (June 2012) blog posting from Mr. Schneier describes why some scams seem so far fetched. In a nutshell, it seems to be an attempt to select only the most susceptible victims. Think what you like, but all of us go through difficult times. When our emotions are torn and we wake up in the morning already weary from the battle, it can be much more challenging to pick out a scam.
Mr. Schneier has written extensively about scams, and security trade offs. You can read more of his commentary on scams here: