An unsolvable problem:
The semi-barbaric King of an ancient land utilized an unusual form of administering justice for offenders in his kingdom. The offender would be placed in an arena where his only way out would be to go through one of two doors. Behind one door was a beautiful woman hand-picked by the king and behind the other was a fierce tiger. The offender was then asked to pick one of the doors. If he picked the door with the woman behind it, then he was declared innocent and as a reward he was required to marry the woman, regardless of previous marital status. If he picked the door with the tiger behind it, though, then he was deemed guilty and the tiger would rip him to pieces.
One day the king found that his daughter, the princess, had taken a lover far beneath her station. The king could not allow this and so he threw the offender in prison and set a date for his trial in the arena. On the day of his trial the suitor looked to the princess for some indication of which door to pick. The princess, did, in fact, know which door concealed the woman and which one the tiger, but was faced with a conundrum. If she indicated the door with the tiger, then the man she loved would be killed on the spot; however, if she indicated the door with the lady, her lover would be forced to marry another woman and even though he would be alive she would never be with him again. Finally she does indicate a door, which the suitor then opens.
At this point the question is posed to the reader, "Did the tiger come out of that door, or did the lady?". The question is not answered, and is left as a thought experiment regarding human nature.
From its publication and surprise ending, "The Lady, or the Tiger?" has come into the English language as an expression, meaning an unsolvable problem. Stockton later wrote a continuation of this story, "The Discourager of Hesitancy".