Sometimes the death of an NPC associated with a quest will result in a pop-up message informing the NPC in question has died, with the quest subsequently failing. The completion of certain quests or tasks will make the NPCs associated with them able to be killed, though most characters integral to the main plot of their respective game are marked as essential permanently throughout gameplay. However, there are still characters involved in quests that can be killed, but most of the time their deaths will result in the quest being failed or proceeding differently. This prevents the player character from breaking the quest and making it impossible to complete by killing an important NPC.
The main purpose of this attribute is to protect the integrity of certain quests which do not account for the death of an NPC important to its progression and plot. This attribute is used in games which use the Gamebryo engine, such as Fallout 3 and Fallout: New Vegas, or the Creation Engine, encompassing both Fallout 4 and Fallout 76.
