Unwinnable by Mistake/Tabletop Games

Examples of in  include:

Dungeons & Dragons

 * Dungeons & Dragons adventure I5 Lost Tomb of Martek. The three Star Gems must be placed in the altar in the Garden of the Cursed so the PCs can continue. However, the Star Gems are also needed much later in the adventure to revive Martek, but there's no way for the PCs to know this. If they assume the Star Gems have fulfilled their purpose and forget to remove them from the altar, they're in trouble. The Crystal Prism area effect that teleports the PCs to the Citadel of Martek only works once. Once they reach the Citadel, even if they use the Teleport wall in the Citadel to return to the Garden of the Cursed to get the Star Gems they can't get to the Citadel of Martek again.