What is a side quest in a video game?

A side quest is an optional mission or activity in a video game that sits outside the main story. You can skip it entirely and still complete the game, but doing so usually means missing out on valuable resources: experience points (XP) to level up your character, unique weapons or armor, in-game currency, or deeper narrative context about the world and its characters.

The optional design is the whole point. While the “main quest” has to carry the heavy load of the central plot — driving the player forward through a structured sequence of major encounters — side quests are where the game developers have room to play. In open-world games specifically (as Gameopedia’s overview of open-world design notes), side quests are what convert the game map from a simple hallway connecting plot points into a living place that rewards exploration and curiosity.

Three reasons why side quests are often the most memorable parts of a game:

• They allow for tonal variety. A main story about saving the world from an apocalyptic threat has to stay relatively serious to maintain its stakes. A side quest in the same game can be absurd, tragic, mysterious, or funny without breaking the main plot’s tension. The Witcher 3’s “No Place Like Home” or Fallout’s strange vault investigations are classic examples where the side content outshines the main story.
• They test experimental mechanics. Developers often use side quests to try out new gameplay ideas — a specific puzzle style, a stealth sequence, a unique traversal mechanic — that would be too risky or annoying if forced onto the player during the main campaign. If the test works, it informs the next game; if it doesn’t, the player can simply skip it.
• They build local depth. A main quest has to focus on the big players (kings, generals, world-saving heroes). Side quests focus on the locals — the tavern keeper, the merchant, the farmer, the eccentric hermit. This local focus is what actually builds “topical authority” for the game’s world, making it feel inhabited rather than decorated.

The psychology behind why players do them is consistent with behavioral-science findings on agency and choice: optional tasks are intrinsically more motivating than mandatory ones. When a game forces you to do a task to progress, it can feel like a chore; when the game offers you the same task as an option, the act of choosing to do it makes the progress feel like your own discovery.

The simpler-not-easier answer covers the physical-world version of this design trade-off — how limiting options in life reduces cognitive load while leaving room for the optional “side quests” that actually make the journey worth taking.

The takeaway: a good side quest is not “filler.” It is the optional space where the game’s world gets its texture, its humor, and its depth. If you only play the main campaign, you might finish the game faster, but you’ll miss the parts that actually make the world feel like home.