The Prisoner's Dilemma

When is our own self-interest best served by going against what reason tells us is our own self-interest?

The prisoner's dilemma is a game theory scenario designed to answer that exact question. The scenario usually looks something like this.

The two teens were caught red-handed, literally. Officer Kotcha just happened to be driving by as the teens launched the brick through the window of the jewelry store. Kotcha's heart rate accelerated as he realized these might be the perpetrators of a string of break-ins throughout the city. Kotcha arrested the boys and took them to the station for questioning.

The officers took the teens to separate rooms and offered each of them the same deal: "We've already got you on the destruction of property, and you'll get a three-month jail term for that. We're ready to charge you with five counts of burglary, which will get you a year each. If you'll confess and plead guilty to the burglaries, we'll make the jail terms concurrent rather than consecutive, so you'll just serve a year. And if you testify against your partner in court, we'll drop all charges against you."

The dilemma the teens face is that, in the absence of knowledge about the other boy's choice, the rational self-interest choice is to betray him. If my partner keeps silent and I keep silent, we serve three months each. But if I confess to the burglaries and testify against him, I walk away free.

If my partner has confessed to the burglaries, on the other hand, I'm getting five years while he gets immunity if I keep silent. But if I confess too, we'll both serve only a year.

Regardless of what the other guy does, I can lessen my own sentence by confessing.

The paradox is that if both teens attempt to protect themselves, they will each spend a year in jail, but if they both go against their self-interest to protect each other, they will cut their sentences by 75%.

This is particulary important if they ever expect to work together again, as we'll see in a later post.