A machine offers you a life that feels completely wonderful. You will never know it is simulated. Would you enter?
Inside, you could write the novel you dream of, mend a friendship, or discover a new world. Each experience would feel real from within. Outside the machine, though, none of those things would actually happen. You would have the feeling of acting, loving, and succeeding, without the events themselves.
Philosopher Robert Nozick used this imagined choice to test the thought that well-being is only pleasure. Hesitating to plug in may suggest that we care about doing things and becoming certain kinds of people, not just how life feels. But the machine is not a knock-down proof: our intuitions can be questioned, and philosophers disagree about what makes a life go well.