"There is a famous conundrum in moral philosophy.
Imagine there is a runaway tram, known in America as a trolley, heading towards five people tied to the track.
You are a bystander.
If you do nothing, all five will die.
But you could hit a switch and divert it down a side track.
Unfortunately, on that spur is one person and if you turn this tram, this person will die.
What should you do? Turn the tram? Most people think you should.
Now imagine that same tram is again heading towards five people. This time you are watching from a footbridge.
There is a fat man leaning over this footbridge. If you push him over, he will land on the track and die, but his bulk will stop the tram.
So should you push the fat man? Almost no-one thinks you should."