Much of the time, however, the needed psychological pressure is self-applied; once the victims have provided money toward the payoff, they feel they have a vested interest in seeing the "deal" through.
Some victims even believe they can cheat the other party, and walk away with all the money instead of just the percentage they were promised.
Another variant of the scam, dating back to circa 1830, appears very similar to what is passed via email today: "Sir, you will doubtlessly be astonished to be receiving a letter from a person unknown to you, who is about to ask a favour from you...", and goes on to talk of a casket containing 16,000 francs in gold and the diamonds of a late marchioness. It then asked what to do with profits from a $24.6 million investment, and ended with a telephone number.
Other official-looking letters were sent from a writer who said he was a director of the state-owned Nigerian National Petroleum Corporation.
Although the vast majority of recipients do not respond to these emails, a very small percentage do, enough to make the fraud worthwhile, as many millions of messages can be sent daily.