“Rock Paper Scissors is Not Solved, In Practice” by Linch

Hi folks, linking my Inkhaven explanation of intermediate Rock Paper Scissors strategy, as well as feeling out an alternative way to score rock paper scissors bots. It's more polished than most Inkhaven posts, but still bear in mind that the bulk of this writing was in ~2 days.

Rock Paper Scissors is not solved, in practice.

When I was first learning to program in 2016, I spent a few years, off and on, trying to make pretty good Rock Paper Scissors bots. I spent maybe 20 hours on it in total. My best programs won about 60-65% of matches against the field; the top bots were closer to 80%. I never cracked the leaderboard, but I learned something interesting along the way: RPS is a near perfect microcosm of adversarial reasoning. You have two goals in constant tension: predict and exploit your opponent's moves, and don’t be exploitable yourself. Every strategy is, in essence, a different answer to how you balance those goals.

Source: https://commons.wikimedia.org/w/index.php?curid=27958688

Simple Strategies

Always Rock

The simplest strategy is to play Rock all the time. This is the move that 35% of human players in general, and 50% of male players, open with.

Rock [...]

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Outline:

(01:24) Simple Strategies

(01:28) Always Rock

(02:36) Pure Random

(03:03) Sidebar: Implementation (for humans)

(03:53) Why isn't Pure Random Perfect?

(04:59) String Finder aka Aaronson Oracle

(05:57) Sidebar: One-Sided String Finder vs Two-Sided String Finder

(06:39) Why Aren't String Finders Perfect?

(07:14) The Henny strategy: Frequency-weighted randomness

(08:31) Henny's Main Limitations

(10:12) Meta-Strategy: Iocaine Powder

(12:26) Strategy Selection Heuristics

(12:41) Random Initialization

(12:57) History Matching

(13:22) Strategy Switching

(13:41) Recency Bias

(13:57) Variable Horizons

(14:11) Database and Evolutionary Attacks

(14:52) Advanced Strategies and Meta-Strategies

(15:10) Better Predictors

(15:30) Improved Meta-Strategy and Strategy Selection

(15:58) Better Game Design

(16:56) Conclusion

The original text contained 8 footnotes which were omitted from this narration.

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First published:
December 10th, 2025

Source:
https://www.lesswrong.com/posts/AGZD62scqRaoM6p4n/rock-paper-scissors-is-not-solved-in-practice

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Narrated by TYPE III AUDIO.

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