In some heads-up games, such as chess and pool, the computer has a huge advantage over the player. Modern chess programs such as Fritz are vastly stronger than nearly all human players.
In pool and snooker games, the computer can be programmed to never miss a shot. However, people want to play against an opponent that is well matched to their skills, and so there are generally levels of AI in the game that the player can choose from.
The simplest way to introduce stupidity into AI is to reduce the amount of computation that it's allowed to perform. Chess AI generally performs billions of calculations when deciding what move to make.
The more calculations that are made (and the more time taken), then (generally) the better the computer will play. If you reduce the amount of calculations performed, the computer will be a worse player.
The problem with this approach is that it decreases the realism of the AI player. When you reduce the amount of computation, the AI will begin to make incredibly stupid mistakes -- mistakes that are so stupid, no human would ever make them. The artificial nature of the game will then become apparent, which destroys the illusion of playing against a real opponent.
Remember what we are trying to accomplish: We want people to have an enjoyable experience. No matter what the game, we want the players to feel challenged so that when they win, they feel a sense of accomplishment. We want them to feel that they were playing against an opponent who was really trying to beat them.
By reducing the amount of computation, we create an AI opponent that is trying to win, but has been crippled in a way that leads to unrealistic gameplay. But does the player actually care about what is going on under the hood? What if we don't cripple our AI, but instead let it play at full strength, but have the AI deliberately throw the game?
In sports, "throwing the game" means one side makes a series of intentional mistakes that look natural, but result in losing the game. This behavior is rightly vilified by players and fans, as the agreement is that there be a contest between two equal opponents, or at least, two opponents who are trying equally hard to win.
But in computer games, it's impossible to have an equal match. It's humans versus machines. One side has an advantage of being able to perform a billion calculations per second, and the other has the massively parallel human brain.
Any parity here is an illusion, and it's that illusion that we seek to improve and maintain via the introduction of intelligent mistakes and artificial stupidity.
The computer has to throw the game in order to make it fun. When you beat the computer, it's an illusion. The computer let you win. We just want it to let you win in a way that feels good.
AI programmers need to get used to this idea. We are manipulating the game, creating artificial stupidity, fake stupidity. But we are not predetermining the outcome of the game.
We don't set our AI with the intent to lose the game, but rather to give the human player a reasonable chance of winning. If the human plays poorly, the AI will still win, but the player will at least feel like she came close to beating a strong opponent, and thus feel like playing one more game.
Computer chess expert Steven Lopez (see Resources) describes how in human versus human chess, it's acceptable for a high-ranking player to give a much lower ranking player an advantage at the start of the game by removing some of his pieces from the board before the game begins.
When the game starts, the master player and the novice player are still playing to the height of their abilities, and yet the game is more evenly balanced. The master player does not have to play "stupid" in order to give the novice player a chance.
However, humans playing against a computer do not like to be given an advantage in this way, and prefer to play the full board against an AI opponent of approximately their skill level.
The programmers of Fritz hit upon a solution that involved the AI deliberately setting up situations that the human player could exploit (with some thought) that would allow the human to gain a positional or piece advantage. Once the human player gained the advantage, the AI would resume trying to win.
At no point here is the AI actually dumbed down. If anything, there is actually quite a bit more computation going on, and certainly more complexity.
The goal of the AI has shifted from "win the game" to "act like you are trying to win the game, but allow the human to gain a one-pawn advantage, and then try to win." The AI needs to be more intelligent in order to appear less intelligent.