Why is tic tac toe so easy? While tic tac toe is an ancient game, it is also a contemporary computer science problem. A tic tac toe program of normal strength can play many games against itself and learn how to always win. “But tic tac toe has three possible moves for each player,” you say, “how can the computer know which move will lead to victory?” There are only nine different outcomes in tic tac toe (excluding draws). Given enough time, the tic tac toe program can determine the best move—and you should see some excitement in these later rounds.
There are indeed only nine different outcomes. But several of these outcomes are “shallow,” and will lead to the same game: both players Xs, or both players Os, or one player Xs and the other player O. These shallow steps can be disregarded for tic tac toe-playing purposes; all that is left are six paths to victory.