Hypothetically:
You are in a room with two other people. You barely know them, but they are kind of nice people. They are both asleep.
Suddenly a lunatic runs in and throws a grenade between the three of you.
Do you push one of them off their bed onto the grenade.
Do you throw yourself on the grenade and save the other two.
Or do you run away.
OK, Think about that and answer it, then look at scenario number 2:
Thanks to modern medicine, we can use your heart to save 1 person, your lungs to save 2 people, your liver to save 1 person, your kidneys to save 2 people.
Lets say that if we killed you now and took you apart, we could save 10 lives with your organs.
Do you sacrifice yourself to save the 10 people?
What if you know one of them is a really nice person and they'll die by the end of the day unless they get a lung?
What if all 10 of those people are nice people who will die without your organs?
In the first case, you save 2 human lives.
In the second case, you save 10 human lives.