The king believes the trial by arena (or choice of the doors) is perfect justice. An accused man determines his own guilt or innocence with one simple decision. Either he chooses the tiger and is promptly killed, or he chooses the lady and is married. The king was quite happy with himself over this administration of justice. Its fairness could not be argued. The accused carried the burden of determining his own fate: 

He could open either door he pleased; he was subject to no guidance or influence but that of the aforementioned impartial and incorruptible chance.

When the princess's lover is accused, however, the king's justice is corrupted. Because this "hot-blooded, semi-barbaric" princess was pleased and happy with her lover, she was particularly interested in his fate. Thus, she asserts her power and gains dominance over her father's arena of justice by discovering the secret of the doors. What had once been an exercise solely based on luck, has now been distorted. Her father's justice is rendered totally subjective, rather than the objective system whereby the accused made his own choice. She becomes the most powerful person in the kingdom, more powerful than even the king.

But, what was her choice? Did she show mercy on her lover and let him fall into the hands of the young lady who was despised by the princess, or did she let him perish in the jaws of the tiger, simply because she could not stand knowing that he had married another? Even though the princess assumes dominance of the doors, it is impossible to know her final decision. Some may argue that true love won out and the door on the right, which the princess pointed to, held the lady. Others may cite her "semi-barbaric" idealism in proving that the lover's fate was death by tiger. Critics have debated the issue for decades.