Fallout co-creator Tim Cain says it's important to leave breadcrumbs of unsolved lore in games so players are interested in it expanding in the eventual follow-ups.
In a YouTube video titled "Leaving Some Mystery," Cain offers some advice: "Don't feel like you need to address every question the player might have." As an example, he says, "In Fallout, we didn't address what Harold was. We didn't need to, wasn't important to the story, isn't important to the setting. It's a fun mystery."
Cain talks about the importance of "leaving some mystery," which he clarifies "means that there's no exposition anywhere in your game by an NPC, or a cinematic, or there's not a book lying around or a computer log entry, that explains it. The team may know the answer, but it's not addressed in the game." And even then, he says, "The reason the team knows is you want to make sure they don't put anything contradictory."
He explains there are two ways to go about it: you could develop a mystery where "there's a lot of evidence in the game that will let the player believe they know what happened, but you never directly tell them." However, Cain also offers "there's another way to do it too, which is just, not develop the lore… "The team doesn't know, the game never mentions it, and the players will never be able to find out in this game."
Cain explains, "The reason you want to put mysteries in your base game is so that you can address them in later expansions and DLC and in sequels," and that "The whole point of having unexplored lore is so that you can explore it later."
He offers advice to aspiring designers, saying that "if you tell everything, players will want nothing." Cain then adds, "It's OK to leave some mystery in it for later exploration or even not for exploration at all. Just leave a little mystery in there. It'll be good for you. People will like it."
