Agatha Christie used to go out at night. She will never forget the night when she met a robber many years ago. That evening, she was invited to a birthday party which lasted till 2 o'clock in the morning. Without company, Agatha walked home along the quiet street. Suddenly from the shadow of a dark building, a tall man with a sharp knife in his right hand ran out at her. "Good morning, lady," the man said in a low voice, "I don't think you wish to die here!""What do you want?" Agatha asked. "Your earrings  . Take them off!"Agatha suddenly had a bright idea. She tried to cover her necklace with the collar   of her overcoat while she used the other hand to take off  both of her earrings, and then she quickly threw them on the ground. "Take them and let me go." she said. The robber was uncertain. He saw that the girl didn't care for the earrings at all, only trying to protect the necklace. He realized the necklace would cost more, so he said, "Give me your necklace." "Oh, sir. It's not worth much. Please let me keep it." "Stop talking rubbish. Quick!" With shaky hands, Agatha took off her necklace. As soon as the robber disappeared, she picked up her earrings and ran as fast as she could to her home. The earrings cost 480 pounds and the necklace the robber had taken away cost only six pounds ten shillings  . Why did she try to protect her necklace?   _  .
She didn't want the robber to notice it. It was cheaper than the earrings. It was worth keeping. She would rather have it robbed.