The trolley problem is a thought experiment. The basic idea is there is a runaway tram or train going down some tracks, heading for five tied-up people. You are standing away from this, next to a lever, but only able to witness the events. If you pull the lever, the carriage will switch to a different set of tracks. However, there is one person tied to this other set of tracks. Do you do nothing and let five people die or pull the lever and let one person die?