Imagine that you are a Doctor.
You have five patients, each of whom has a terminal illness, each in a different major organ of the body. Without transplants from suitable donors they will certainly die.
Now, another patient comes in for a routine check up and in the course of this you discover that they are a perfect match for each of the five other patients respectively, and that by taking their organs and transplanting them, you will have a 100 per cent certainty of saving those five people. The one donor patient will die.
What should you do?