Zero Sum Game
If you know what you are doing, you can't lose at Tic-Tac-Toe. If your opponent knows what they are doing, you can't win at Tic-Tac-Toe. The game is a zero sum game. If both players are playing with an optimal strategy, every game will end in a tie.
Surpisingly few people know optimal Tic-Tac-Toe stategy. Yes there are some people (and computers) that you will never beat, but they are relatively rare. Knowing this, you can become a Tic-Tac-Toe master.