A riddle in the dark

The young villager stood before the towering sphinx, his heart pounding in his chest. It was a giant creature, with the body of a lion and the head of a beautiful woman, her features wise and crowned by a small golden band. Her fur was a deep golden brown, and her eyes were as black as the void between stars.
With a voice that was equal parts rumbling stone and purring of a giant cat, her words echoed through the dusty, ancient tomb:

What can bring back the dead;
make you cry, make you laugh,
make you young;
is born in an instant,
yet lasts a lifetime?"

The sphinx's dark, fathomless eyes stared expectedly at the young adventurer as he stood before her, his brow slick with sweat. The young man swallowed hard. He thought he could find the answer , but he was afraid to speak. He had heard the stories, and all knew what fate awaits those who answer a sphinx wrongly.
He looked around the tomb, his eyes darting around the area dimly lit by his torch. The walls were covered in hieroglyphics, telling the stories of ancient gods and heroes. The air was thick with the smell of mildew and decay, and the only sound was the dripping of water from somewhere deep within the tomb.
The sphinx's dark eyes fixed on him. "Think long and hard on your answer, humanling," she said. "For I am honorbound to devour you if you answer falsely."
The young adventurer took a deep breath. He closed his eyes and concentrated. He thought about all the things that could bring back the dead, make you cry, make you laugh, and make you young.
He thought about the memory of his mother's smile, the sound of his father's laughter, and the feeling of his first love's kiss. He thought about the pain of losing his loved ones, and the joy of seeing them again in his dreams.
Suddenly, he knew the answer. He opened his eyes and looked at the sphinx.
"Memory," he said.
The sphinx's eyes widened, her black gaze staring at him intently. "Memory?" she repeated. "That is your answer?"
The young man nodded. "Yes," he said. "Memory can bring back the dead in our minds. It can make us cry, make us laugh, and make us feel young again. It is born in an instant, yet it can last a lifetime."
The sphinx nodded slowly. "You are correct," she said. "You have passed the test."
The sphinx massive form stepped aside, allowing the young man to pass. He took a deep breath and started running, his torch held high in one hand.
As he ran, the young man thought about the sphinx's riddle. He realized that she had not just been testing his knowledge; she had also been testing his courage. Afraid to respond to her question at first, he had faced his fears and passed the challenge. In doing so, he had proven himself to be worthy to her.
A few moments later the entrance was in sight and he stumbled out into the starry night. He took a deep breath of the cold night's air and looked back. And there, in the shadows of the tomb's entrance, the sphinx stood, her dark eyes watching him intently.
The young man nodded his head in a gesture of respect and gratitude. Then, he turned and ran into the desert night, leaving the sphinx, the tomb and this story behind him.