system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: What does it mean that a situation is a prisoner’s dilema?
gpt
The classic prisoner's dilemma is that two suspected criminals are being questioned separately (so they can't communicate with one another). If they both stay silent, they'll serve 1 year in prison. If they both turn on each other, they'll both serve 5 years in prison. If one turns but the other stays silent, the one that turns will get off free, but the other will serve 8 years.

In this example, the best thing to do for both criminals together would be cooperate, because it provides the fewest total years served (only 2). However, to an individual criminal, turning on the other is always better. If he stays silent, you get off completely, and if he was planning on turning on you, you only get 5 years instead of 8. This results in two perfectly rational criminals turning on one another and getting the maximum 10 years of total prison time.

So a true prisoners dilemma requires two or more people to make a decision where, collectively they'd be best to choose A, but individually they'd be best to choose B every time or almost every time. A common example shows up in post-apocalyptic stories where groups would be best served working together, but each group tries to grab a little more of their share each time, leading to infighting and eventually killings and territoriality.

Does that help? Feel free to ask any questions.