It is a game where you simultaneously choose whether to "cooperate" or "defect." When you try to maximize your score without knowing the other player's choice, you tend to choose mutual defection.
For each player, defection is always the safer choice (no matter what the other player does, defecting gives you the same or a higher score). But if both follow this logic, they get lower scores than if they both cooperated. This situation is called a "Nash equilibrium."
| Opponent: Cooperate | Opponent: Defect | |
|---|---|---|
| Me: Cooperate | Me 3 / Opponent 3 | Me 0 / Opponent 5 |
| Me: Defect | Me 5 / Opponent 0 | Me 1 / Opponent 1 |