CW: Suicide, death
You find yourself confined to a glass box with a gun placed directly against your left temple. Ahead of you is a small metallic cylinder with a small coloured light about two-thirds of the way up. A few wires exit the top of the cylinder and feed into a box below. You follow a set of red and black wires twisted together emerging from the box. They travel past your left foot, taped along the side of the makeshift laboratory and up the adjoin between two of the glass panels, into a small mechanism attached to the trigger of the gun.
The experiment is clear. Something takes place within the cylinder. If the right thing (or rather, the wrong thing) occurs, you immediately and unequivocally die.
It is, in fact, a quantum measurement that takes place inside the cylinder. The details of the measurement are unimportant, other than there is a 50% chance of measuring either of two possible states that, prior to measurement, exist in a quantum superposition. The nature of quantum superposition is such that the state of the quantum system — the spin of an electron, for example — is simultaneously both states at once.
Upon measurement, the state of the system is unambiguously either one state or the other. This is the function of the light on the cylinder. A small green flash indicates a measurement of the first state. However, the second state is characterised by the slightly more grim flash of a gun.
The light flashes green. Success.
Not surprising, however. The experiment repeats. Green light. Lucky but, again, not amazing. Then it happens again: green light. The experiment has now been repeated thrice with just as many successful outcomes. Then it happens again, and again… and again. After a few minutes, you have lost count of the measurements and subsequent green lights. Your colleagues pressed to the glass outside have started to take an interest in your borderline insane experiment.
You could call it luck, but at this point, the chance of a single — and final — unsuccessful trial should almost certainly have occurred. With the same luck, you could have won the lottery twice with tickets that landed on your cereal through an open window, thanks to a perfectly timed gust of wind travelling…