A little boy had a sister who needed a blood transfusion. The doctor explained that the sister had the same disease the boy had recovered from two years earlier. Her only chance for survival was a transfusion from someone who had previously conquered the disease. Since the two children had the same rare blood type, the boy was the ideal donor.
"Would you give your blood to Mary?" the doctor asked.
Johnny hesitated. His lower lip started to tremble. Then he smiled, and said, "Sure, for my sister."
Soon the two children were wheeled into the hospital room--Mary, pale and thin; Johnny, robust and healthy. Neither spoke, but when their eyes met, Johnny grinned.
As the nurse inserted the needle into his arm, Johnny's smile faded. He watched the blood flow through the tube. With ordeal almost over, his voice, slightly shaky, broke the silence, "Doctor, when do I die?"
Only then did the doctor realize why Johnny had hesitated, why his lip had trembled when he'd agreed to donate his blood. He'd thought giving his blood to his sister meant giving up his life. In that brief moment, Johnny had made his great decision.