Dorian and Abigail play a game of tic-tac-toe. Dorian plays with crosses (x) and Abigail plays with noughts (o). However, we do not know who amongst Dorian and Abigail started this game.
In the game shown below, six moves have already been made:
o | o |
---+---+---
o | x |
---+---+---
x | x |
Who will win the game?
Tic-tac-toe, with errorless play, always results in a draw. Since the next player to move can win, we know that at least one player has made an error. Therefore, there is no way to tell who played first with absolute certainty. All we know for sure is that there has been some bad play.
One can make some inferences if one assumes, for instance, that even a very bad player will complete a three-in-a-row when it is available, or will block the other player's three in a row, but I don't see any reason to make that assumption. I choose to believe that all losing plays are equally bad.