Simple Rules

Definition

Simple rules are shortcut strategies — rules of thumb — that people, organizations, and even animals use to make decisions and take action quickly under limited time and information. Sull and Eisenhardt argue that effective simple rules always share four traits: they are limited to a handful (so they can be remembered and force focus on what matters most); they are tailored to the specific person or organization using them rather than universal; they apply to one well-defined activity or decision rather than many (rules that try to cover everything collapse into vague platitudes); and they provide concrete guidance while still leaving room to exercise judgment, rather than dictating a single prescribed action.

In the Book

The book opens with combat medics and frontline triage — Sergeant Montoya sorting casualties after a Mosul mess-tent bombing using a handful of vital-sign rules, and the color-coded triage system used from the Boston Marathon bombing to flu-pandemic vaccine allocation — to show simple rules working under extreme time pressure. Chapter 1 then contrasts the Jesuits with the Benedictines and Dominicans: those older orders governed every member's life through constitutions running to hundreds of highly detailed regulations (down to how many dishes could be served at dinner), while the Jesuits' founding "Formula" was five paragraphs long. That handful of rules — go wherever assigned, favor education, skip communal prayer — gave the Jesuits the flexibility to expand from ten founders to a thousand priests across four continents within two decades, while more heavily regulated orders stayed local and small. The chapter also contrasts Michael Pollan's "Eat food. Not too much. Mostly plants" and a Moscow private-equity firm's investment screening rules (revenue between $100M–$500M, in an industry the firm already knew, run by executives who "knew criminals but weren't criminals themselves") against a rival Russian bank's vague guidelines like "Invest in undervalued companies" — vague platitudes that junior bankers dismissed as useless.

Why It Matters

Simple rules resolve a genuine trade-off that most decision-making advice ignores: total discretion produces inconsistency and slow deliberation, while total prescription (a detailed procedure or algorithm for every case) produces rigidity that can't adapt to unanticipated situations. A well-formed simple rule sits between these poles — narrow enough to be actionable and memorable, loose enough to leave room for judgment on the specifics. That combination is what lets it work in domains as different as wartime medicine, religious-order governance, sports nutrition, and investment screening, and it gives a concrete standard (few, tailored, bottleneck-specific, guidance-not-dictation) for judging whether any given rule, policy, or guideline you're handed is actually a simple rule or just a platitude in disguise.