Kindle and paperback
You know the famous thinking tools. Do you know which ones work?
Mental Models That Actually Work is a book by Ada Fenwick that traces forty thinking tools credited to Munger, Bezos, Feynman, Kahneman and others back to their original sources and checks each one against the research. Every tool gets an evidence badge and a short card you can use on a real decision.
Mental Models That Actually Work. 40 Thinking Tools from Munger, Bezos, Feynman, and Kahneman, Tested Against the Evidence, for Clearer Thinking and Better Decisions
You've seen the lists. First principles. Inversion. Second-order thinking. Circle of competence. Each one comes with a famous name and a tidy quote. After a dozen articles about them, you still make the same call you would have made anyway.
Part of the problem is that thinking tools get passed around like jokes. Each retelling drops a detail and adds a famous name. "Show me the incentive and I'll show you the outcome" is credited online to a famous investor's 1995 Harvard talk, yet a text search of both versions of that talk finds no such sentence. If the quote is shaky, how sure can you be about the tool?
This book sorts the pile. Forty tools, each traced to the letter, speech, book or paper it came from, and each graded SOLID, PROMISING or STORY ONLY. The book's own count is 6 SOLID, 20 PROMISING and 14 STORY ONLY. Some famous tools landed lower than you'd expect. Some modest ones, like writing an if-then plan, landed higher.
Every tool fits on a card: steps, when to reach for it, what the science says, and what to write in your Decision Log. If you have a choice to make right now, start with the Decision Selector at the back. Weeks later, write down what happened. A good decision can still turn out badly, and only a written record shows you the difference.
Why don't mental models change how you decide?
- Quotes without sourcesFamous names get attached to lines nobody can find in the record.
- Tools without evidenceMost lists never say which models were tested and which are just habits of successful people.
- Right tool, wrong decisionA slow, careful method on an easily reversed choice wastes time, while a quick call on a choice you can't undo can cost far more.
- Judging by outcomesWithout a written record, memory is generous, and you remember being more right than you were.
What's inside the five parts
- 01Part I: See the situation clearlyFirst principles, the map and the territory, circle of competence, inversion and second-order thinking.
- 02Part II: Think in probabilitiesThe outside view, calibration, updating and expected value. In forecasting tournaments, less than an hour of probability training improved accuracy by 6 to 11% (Chang et al., 2016).
- 03Part III: Catch your own errorsConsider the opposite, the pre-mortem, steelmanning and red teams, razors and sunk costs. The book traces the popular "pre-mortems improve accuracy by 30%" claim to a 1989 study that counted reasons, not correct answers.
- 04Part IV: Decide and actOne-way and two-way doors, regret, good enough and the 37% rule, checklists and if-then plans, and decision journals.
- 05Part V: Thinking with othersIncentives, why everyone should guess alone before anyone talks, and how to hear the argument nobody wants to make.
- 06Tools at the backA one-page Decision Selector, a 30-day plan, Decision Log pages and a calibration tracker.
What changes when you face the next decision?
You stop collecting mental models and start using a few. Facing a choice, you know which tool fits it, how much evidence stands behind that tool, and what to write down so you can check yourself later. Over months, your Decision Log shows where you tend to be overconfident. No tool removes uncertainty. You just handle it more deliberately.
This book is for you if
- You've read about mental models and want to know which ones hold up
- You make real decisions at work or at home and want a repeatable process
- You care about sources and distrust quotes with no record behind them
- You want short tool cards you can come back to, not just theory
This is not the book for you if
- You want someone to tell you what to decide. The book teaches ways to think about decisions, not answers.
- You're looking for investment picks. Nothing in it is financial, investment, legal or medical advice.
- You want a list of hundreds of models with a paragraph each. This book goes deep on forty.
Questions about Mental Models That Actually Work
What format is the book?
It is available in English as a Kindle ebook and a paperback on Amazon. The Kindle edition is included in Kindle Unlimited. In the paperback you can fill in the log pages directly; on Kindle, copy the fields into a notebook.
What do the badges mean?
SOLID means tested on people more than once or backed by a review that pools many studies. PROMISING means real but thin or indirect evidence. STORY ONLY means a real, documented practice nobody has properly tested. MYTH is never given to a tool, only to a false quote or origin story.
Where should I start?
If you have a decision in front of you, start with the Decision Selector at the back. It matches common situations to the tools that fit them. If you like structure, follow the 30-day plan, which starts with easy, low-stakes drills.
Is this financial or investment advice?
No. The book states it is not financial, investment, legal or medical advice. The chapter on expected value shows how to weigh outcomes, not what to buy. For money, health or legal decisions, it suggests asking a qualified professional.
How long is the book?
Amazon lists a print length of 300 pages for the Kindle edition. The tool cards are short on purpose, so you can return to them when a decision comes up.
