You were doing it all wrong! :-P

Actually, that is the mistake.

Tic-Tac-Toe is easy to solve; in this game, the result will be a tie if both players are playing optimally.

Connect Four has been solved by computer program; I believe the result is the first player always wins.

Chess has not been solved; because one player's move can make other moves by the other player possible (something not the case in Tic-Tac-Toe), it's not safe to assume that the result isn't "player 2 always wins".

A board game called "Go" is apparently much harder than chess.

Some versions of the game "Nim" are guaranteed wins for the second player.

The game where there are 21 tokens, you take 1 to 4 on your turn, and whoever takes the last one *loses* is a win for the second player. (Interestingly, Super Mario RPG puts you into this situation at one point, but the AI is (deliberately) imperfect, so once it makes a mistake, you can easily win.)

Anyway, here is a relatively simple programming exercise: Write a program that plays Tic-Tac-Toe optimally. It should never lose, regardless of what the other player does.

For actually playing the game, however, it would be more fun to play against a program that plays randomly rather than optimally.

Player 1 choosing middle is always a draw. Player 1 choosing a corner however can result in a win if Player 2 won't choose the middle.

I agree. O would be trying to complete their line, but not while also blocking. You want to block and attack at the same time in TTT.

Well, I guess if you take a broad enough definition of 'mistake', then the OP strategy doesn't even need to be stated other than two words: "play optimally". I think the scenario I gave would be a way someone who was following the strategy for O ("If you're O, start in a corner.") could easily lose.

You are correct. Playing optimally involves staying off the sides and there are still ways to lose if you leave yourself open.

Nonetheless, if you know an 8-year-old who's anxious to play some tic-tac-toe, you'll know how to play as O to let them win every time. And then they'll think they're awesome. Because they are.

That's only true if player 1 is playing rationally. If player 1 deliberately avoids blocking player 2, player 2 will win.

Why would he avoid blocking and thus loose. Even as a 5th grader i knew i don't want to do that.