A quest is an adventure game that requires the player to solve mental problems to progress through the story. It's basic. The situation with more than one story line, etc., we will not consider.
That is, the impact on the world and surrounding objects, is done by indirect influence. If in FPS, it's the opposite - the player drives the story with shock action, he is a catalyst for events, then in the quest, more often than not, due to either deliberate weakness of the hero, or the lack of a component of aggressive action in general, the player must act by stealth.