It's good to donate blood to others in need.
Carl is driving by a blood donation tent.
Carl wants to contribute to the cause.
Carl stops and donates Carl's rare blood even though Carl is uncomfortable with needles.
Carl honks his horn and gives a thumbs up sign at the tent as Carl drives by without stopping.
Someone in need can receive a blood transfusion and continue living.
A child with Carl's exact rare blood type dies because the child cannot get a transfusion.