Suppose this one has to be pitched...
SYNOPSIS: There is a large button in public display. Place considerable amounts of material stressing, very clearly, that NOTHING BAD WILL HAPPEN if the Button is pressed.
The Button is behind bullet-proof glass. Two years in, the glass automatically removes itself.
HYPOTHESIS: The presence of the Button, combined with the extreme propaganda of "nothing bad will happen", will most likely convince people something bad WILL happen. The button shall therefore be kept off-limits.
SYNOPSIS: As above, but the Button causes the entire Vault to self-destruct, killing all inhabitants.
HYPOTHESIS: I give it a week.