Constantinos Daskalakis is a mathematician who proved a very important theorem in game theory. The theorem is about something called the Nash equilibrium.

The Nash equilibrium is a concept in game theory that helps predict what people will do in a game. It's a situation where each player is doing the best they can, given what the other players are doing. In other words, no player can do better by changing their strategy, assuming the others don't change theirs.

For example, let's say we have a game where two players have to choose between two options: A or B. If Player 1 chooses A, and Player 2 chooses B, then Player 1 gets a reward of 3 and Player 2 gets a reward of 1. If both players choose A, they both get a reward of 2. If both players choose B, they both get a reward of 1. In this game, the Nash equilibrium is when both players choose A, because neither player can do better by changing their strategy, assuming the other player doesn't change theirs.

Daskalakis proved that computing the Nash equilibrium for a three-person game is very difficult, which means it's not practical to do it using a computer.