This post isn't as evil as it sounds because it's yourself you'll be tormenting. The method you will use is counterfactual thinking. If you use it right, you can wring money from the gullible and improve all kinds of things about yourself... just not necessarily in that order.
Poetry, Psychology, and Counterfactuals
When poet John Greenleaf Whittier wrote "For of all sad words of tongue or pen, the saddest are these, 'It might have been'", he was describing a counterfactual — the line of thinking we take when we imagine how a sequence of past events might have been turned in some other direction. Whittier was right in estimating a human being's capacity for regret, but he clearly didn't have a handle on a human being's taste for the morbid. We frequently think about all the awful things that could have happened to us if we had changed just one thing, and that makes us feel pretty good.
Psychologists have studied counterfactuals and their effects on our attitudes. The most famous study of counterfactual thinking was performed by Daniel Kahneman and Amos Tversky, who got people in a room and spun this little yarn:
"Mr. Crane and Mr. Tees were scheduled to leave the airport on different flights, at the same time. They traveled from town in the same limousine, were caught in a traffic jam, and arrived at the airport 30 minutes after scheduled departure time of their flights. Mr. Crane is told that his flight left on time. Mr. Tees is told that his flight was delayed, and just left five minutes ago. Who is more upset, Mr. Crane or Mr. Tees?"
Everyone agreed that Mr. Tees should be the more pissed-off of the two. Even though they were both equally not-on-their-planes, Mr. Tees should be tormenting himself with thoughts about how, if only he had started a few minutes earlier, or if only he had taken the train, he'd be in the sky. That's a sad "it might have been."
But it's not nearly as sad as winning a silver medal. Another study compiled clips of silver medalists at the Olympics, both just after their win and on the podium, and had subjects analyze the winner's expressions. The subjects believed that most silver medalists were sad, having just missed out on gold. This sentiment was reinforced when psychologists asked people who came in second place at important (but not Olympic level) sporting competitions. The general sentiment was, "I might have been first."
Not so when it came to bronze medalists or people who placed third in major sporting events. They were relatively happy, according to both the people analyzing their expressions and the athletes themselves. They "might have" not even placed. They were "that close" to being shut out of the next round of competition, or out of history altogether. Because of their comparatively gloomy counterfactuals, third place winners were often happier than second place winners.
Profit, Psychology, and Counterfactuals
Even counterfactuals that make us unhappy aren't all that sad. Unlike Olympians, we don't get only one shot at gold. When we can try again, counterfactuals can be very helpful, as a study that had people apply counterfactuals to their performance on a test found. Granted, the stakes were low; subjects were asked to play an anagram game, and were given or generated "upward and downward" counterfactuals. Downward counterfactuals were the usual "you might have done even worse than this" reassurance, and they made people feel better about themselves, while upward counterfactuals increased their determination and helped them improve their performance on subsequent tests.
In other words, an "upward counterfactual" is that most basic of problem-solving strategies, figuring out your mistakes and thinking about how to avoid repeating them. While there is a bit of regret involved, it's a spur to do better. "It might have been" is only sad when it can't be followed by "so let's give it another whirl."
There's another use for counterfactuals, and it's mercenary. A study in which subjects had to decide the proper financial compensation for victims of various unpleasant scenarios proved that counterfactuals can be lucrative. When reading victims of accidents or crimes with normal background stories, the study subjects recommended normal amounts of compensation. Then they read about the tear-jerkers: People who would have married their true love, if only that person weren't torn from them when a hurricane hit the Tunnel of Love at the fair, and people who got a scholarship to a dance academy then lost their foot in a car wreck on the way there. The power of "it might have been" was strong, and the study subjects awarded them significantly more compensation. So if something terrible happens to you, tell people how it kept you from the happiest possible circumstance — then await your compensation.