Chaosu: You are incorrect, since white can win 5-in-line if black makes an error.

However in Backgammon situations arise where no matter how the dice are played it is impossible for one player to win. This is the case when you should resign.

For instance if you have borne off one piece and your opponent has 6 pieces on point 1 then you cannot possibly win no matter what, so there is no reason whatsoever to make another move... just resign and move on to the next game or start another.

grenv: But we were talking mainly about go, You did not mentioned Backgammon case before... Also, if someone is new to the game he will like to play it until end to learn more/understand whats happening. In the meantime You will sit next to Your comp and yell 'why he does not resign', yes?

And about gomoku, yes thats true, this is probably reason why players play even when opponen thinks that he won.