She was 40. She was tired. She felt tired all the time. She went to the doctor. The doctor asked, "What's the matter? What's your problem?" She said, "I'm tired. I feel tired all the time." The doctor examined her. The doctor asked her a lot of questions. The doctor asked for a blood sample. He took some blood from her arm. The doctor asked for a urine sample. He told her to pee in a cup. A week later, the doctor called her. He said, "Your samples are okay. There is nothing wrong with you. You are tired because you don't exercise. You need to exercise. Take a walk every day. Ride a bike every day. Walk up stairs every day. If you exercise, you won't feel tired." She didn't believe her doctor. She didn't exercise. If I exercise, she thought, I will feel even more tired.