the.com/trolley problem

means A thought experiment that asks whether it's right to actively divert harm toward one person if it saves a greater number of people, used to probe the difference between killing and letting die.

from Introduced in 1967 by philosopher Philippa Foot in a paper on the ethics of abortion, using a runaway trolley headed for five workers, with a lever that could divert it onto a track with just one. Philosopher Judith Jarvis Thomson later expanded the scenario in the late 1970s, adding variants like pushing a bystander off a bridge to stop the trolley, which sharpened the puzzle into the form most people argue about today. What began as a narrow tool for analyzing moral reasoning escaped into popular culture, becoming shorthand for any impossible ethical choice.