The princess used her power, influence, and force of character to find out who was behind the door.
In this kingdom in the “very olden time” in which the story takes place, a semi-barbaric king is running the show with his very unique sense of justice. He essentially believes that his court is just because it leaves things up to fate. The victim has to choose between two doors, and if he chooses the wrong door, he must be guilty.
It makes a strange kind of semi-barbaric sense, if you believe in superstition. Either way, the audience is entertained. They get to see either a bloody execution or a fun wedding.
The whole thing takes on a personal touch when the king’s daughter is involved. Her lover gets thrown on the mercy of the court, and now things are not quite put to chance anymore. First of all, she does not want to leave things up him. Second of all, she is too curious. She wants to know what door will have what, and who the lady will be.
Possessed of more power, influence, and force of character than any one who had ever before been interested in such a case, she had done what no other person had done - she had possessed herself of the secret of the doors.
Now, as with a lot about this story, I realize this is somewhat ambiguous. Does the princess use her feminine wiles in order to get the information? It is possible? However, the author also says she has power and influence, in addition to the very vague “force of character.” So we can assume that she did that, given her personality and the situation that got her here, but I will let you draw your own conclusions.
Once she determines who is behind the door, and what is behind which door, the princess also gets to make a choice. If she tells her lover to pick the tiger, he will die but she will not have to watch him with another girl. She does not seem to like that idea.
How her soul had burned in agony when she had seen him rush to meet that woman, with her flushing cheek and sparkling eye of triumph; when she had seen him lead her forth, his whole frame kindled with the joy of recovered life…
If she tells him to pick the lady, she can run off with him and tell him to forget the lady. After all, she has force of personality! The ending is ambiguous. We do not know what door she picked. The author tells us we can find the answer in human nature. I think though, that we found our answer in that last quote.
Stockton seems to think this story is a personality test. If you are a pessimist, you believe that she picked the tiger. If you are an optimist, you believe that she picked the lady. I think that you can have a more complex view of human nature that that. Do you?