Abstract
Problem: When should game developers use randomness, and how does it interact with save systems?
Approach: Tim Cain draws on decades of RPG development experience (Fallout, Arcanum, The Outer Worlds) to explore where randomness works, where it breaks down, and what alternatives exist.
Findings: Randomness exists in tension with save-anywhere systems — players will save-scum to defeat RNG. The solution is either restricting saves, restricting randomness, or replacing it entirely with deterministic alternatives like player stats, player behavior, timers, or minigames.
Key insight: Most game developers who ask for "randomness" don't actually want true randomness — they want fairness, uniformity, and cyclic behavior. Understanding this distinction is crucial for good system design.
1. Why Use Randomness?
Randomness makes games vary, feel unpredictable, and adds replayability. Common applications include:
- Hit determination — whether an attack connects
- Damage ranges — so attacks aren't identical every time
- Skill checks — lockpicking with a percentage chance of success
- Random encounters — meeting different enemies on a world map
- Loot tables — randomized drops from non-boss encounters
- Merchant inventory — shops that don't always stock the same items
2. The Tension With Save Games
Randomness exists in fundamental tension with save systems, particularly save-anywhere games. Players will simply reload until they get the result they want: save before a locked door, fail the pick, reload, try again until it works.
This is why randomness works in some games but not others — it comes down to two factors:
- Some games restrict where they use randomness
- Some games restrict where saves are allowed
The more randomness a game uses, the less it should allow unrestricted saving — and vice versa.
2.1. Restricted Saves
When saving is limited to the start of a map or designated rest points, randomness works much better. Players must replay significant portions of the game to re-roll outcomes, making save-scumming impractical.
2.2. Restricted Randomness
Not every system needs a random roll. The Outer Worlds handled melee attacks this way: if you're facing a target within range, your melee attack always hits — but your skill determines how much damage you deal. Similarly, merchants can be given slow refresh timers so players can't rapidly reroll their inventory.
3. Alternatives to Randomness
3.1. Pre-Rolled Random Numbers
Generate future rolls in advance and store them on the player character. Arcanum did this for skill checks — the next skill roll was saved on the character. However, savvy players learn to "burn" unfavorable rolls by using a different skill first, then reloading and attempting the check they actually care about.
3.2. Random Seeds
Store just the seed for a linear congruential generator. Arcanum used the player's character name as the seed for chest loot generation — making even your name choice matter. Tim also used this in the GURPS star system generator, where an entire galactic sector was stored in just four bytes (the seed), giving roughly 4 billion unique sectors.
3.3. Player Stats as Determinism
Replace random checks with stat thresholds. If your stealth is high enough, you can always sneak past. If your luck meets a minimum, special encounters trigger. Fallout's random encounters used luck this way. The outcome isn't random — it's deterministic based on character build — but different characters still get different experiences.
3.4. Player Behavior as Triggers
Killing a particular NPC, stealing an item, or choosing a specific dialogue line can set triggers for events that fire days or weeks later. It may feel random to players, but it's entirely causal. This creates organic replayability — "my playthrough was different from my friend's because we made different choices."
3.5. Timers
Events fire on fixed intervals. The apparent randomness comes from when the player happens to be present. One player enters a town and an event fires 5 seconds later; another enters and waits 5,000 seconds. Since you don't control the player, they become an interesting source of pseudo-randomness.
3.6. Minigames
Replace random skill checks with player-skill-based minigames (lockpicking puzzles, hacking interfaces). Character skill can make the minigame easier or harder. Tim notes the tension here: your character may be a master lockpick, but if you are terrible at the minigame, the character effectively isn't — divorcing player skill from character skill in an RPG.
4. Summary
Randomness makes games less predictable and more replayable, but depending on the player, that can be good or bad. The key design considerations are:
- Match your randomness approach to your save system
- Consider whether you actually need RNG or whether deterministic alternatives serve better
- Remember that "randomness" in design discussions usually means variety and fairness, not true statistical randomness
5. References
- Tim Cain. YouTube video. https://www.youtube.com/watch?v=w2hohAXhfLU