Arrow's Impossibility Theorem
No ranked voting system satisfies a short list of obviously reasonable conditions. Applies directly to prioritization, ranking, and consensus UX.
Systems-Design
The End-to-End Argument
Functions belong at the endpoints; lower layers can only optimize, never guarantee. The single most useful design principle in networking.
Saltzer and Schroeder's Principles
Least privilege, fail-safe defaults, economy of mechanism; plus the confused deputy as the canonical violation.
Competitive Analysis and Ski Rental
How to reason about decisions made without the future, with a provable ratio. Rent-vs-buy shows up in caching, autoscaling, and connection pooling.
Token Buckets, Arrival Curves, and Network Calculus
Rate limiting has a theory: bound the arrival curve and you get a provable bound on delay and queue depth.
Latency Under Utilization
The M/M/1 queue's 1/(1-rho) blowup. Why a service at 80% load is fine and at 95% is on fire.
Little's Law
L = lambda W, with essentially no assumptions. Capacity planning from one line of algebra.
The CAP Theorem and PACELC
What it actually says, why it's routinely misquoted, and why latency (the "ELC") is the part that governs real designs.
Conway's Law
Systems mirror the communication structure of the organizations that build them. Empirical, not proven — and the inverse maneuver as its practical use.
Hyrum's Law and Postel's Principle
Every observable behavior of your API is depended upon by someone; and the robustness principle that made that worse, plus the modern case against it.