I recall a story told by a priest in a sermon at Mass many years ago. There was a boy who was very ill, and he had a rare blood type. Donors were scarce, and so the doctors had to ask the family if his younger sister could donate some blood. The parents carefully explained the situation to the girl, and when they thought that she had understood, they asked if she would be willing to give some of her blood to her brother. She agreed. The procedure to donate some blood was completed, and then they asked the girl if she had any questions. She had only one question: “When do I die?” She thought, by agreeing to give her blood to her brother, that he would live and she would die. And yet she consented.
— Quoted from my book Forgiveness and Salvation for Everyone