Deductive Reasoning

One-Line Definition

Starting from a general premise, reaching a specific conclusion through logical reasoning.

Core Concept

Deductive reasoning derives specific conclusions from known general principles. The classic form: major premise → minor premise → conclusion. If the premises are correct and the reasoning is valid, the conclusion is necessarily correct.

What Problems It Solves

When information is incomplete, options are numerous, or risks are unclear, it helps you shift judgment from intuition to structured analysis.

Deep Work

One-Sentence Definition

Deep Work is the practice of protecting uninterrupted attention for cognitively demanding tasks that create durable value.

TL;DR

• Deep Work is the practice of protecting uninterrupted attention for cognitively demanding tasks that create durable value.
• Use it to make judgment more concrete and less reactive.
• Apply it with clear evidence, boundaries, and next actions.

What Problem Does It Solve?

Deep Work solves fragmented attention. Modern work rewards quick replies, meetings, tabs, and context switching, but many valuable outputs need sustained reasoning.

Deliberate Practice

One-Line Definition

Enhance abilities through clear goals, feedback, and iterative refinement.

Core Concept

Help you gain faster feedback, correct your approach, and build lasting competence.

More specifically, Deliberate Practice is suitable for answering questions like: Is what I’m seeing now a fact, an assumption, or a habitual response? To make a better choice, which variable, path, or constraint should I examine first?

When to Use

• When the problem becomes complex and intuitive judgment is not reliable enough.
• When the team disagrees on the next steps and needs a shared analysis framework.
• When you need to turn abstract judgments into concrete actions, checklists, or experiments.
• When current approaches are yielding diminishing results and you need to reexamine the underlying logic.

When NOT to Use

• When the problem is simple and direct execution is more important than analysis.
• When basic facts are missing and you are only spinning conceptual wheels.
• When using the model is only to justify existing conclusions rather than to help correct your judgment.
• When the stakes are extremely high, trial and error is impossible, and there are no additional verification methods.

How to Apply

1. Write down the current problem: Describe in one sentence what you need to judge or resolve.
2. List existing assumptions: Distinguish among facts, opinions, experiences, emotions, and default answers given by others.
3. Identify key variables: Find the 1–3 factors that most influence the outcome.
4. Form alternative actions: Propose several different approaches based on the key variables.
5. Define a minimum viable test: Use a low-cost action to verify which judgment is closer to reality.

Example

Suppose a team finds that the new user conversion rate is declining. When using Deliberate Practice, they don’t immediately ask a designer to change a button or have operations increase the budget. Instead, they break it down: Where do users come from? What information do they see? At which step do they hesitate? What is lost when they abandon? Is there a stronger alternative? After this breakdown, the team might discover that the real issue is not insufficient traffic, but that users don’t understand within the first screen what problem the product solves. So the minimum viable action is not redesigning the entire product, but first testing a clearer value proposition.

Dimensional Strike

One-sentence Definition

Launching competition from a higher dimension, leaving lower-dimensional opponents unable to respond.

Core Concept

A dimensional strike uses higher-dimensional capabilities, resources, or perspectives to solve lower-dimensional problems or competition. It’s like how the three-dimensional world can easily resolve difficulties on a two-dimensional plane.

What Problem Does It Solve

When information is incomplete, options are many, or risks are unclear, it helps pull your judgment back from intuition to structured analysis.

Dimensional Thinking

One-Line Definition

View problems from a higher dimension, breaking through the limitations of the current level.

Core Concept

Dimensional Thinking is about elevating a problem from a lower dimension to a higher dimension to solve it. Problems that seem unsolvable at a lower dimension may be easily resolved when viewed from a higher dimension.

What Problems It Solves

When information is incomplete, there are many options, or risks are unclear, it helps pull your judgment from intuition back to structured analysis.

Counterevidence Thinking

One-Sentence Definition

Actively seek evidence that can disprove your own viewpoint.

What Problem Does It Solve

It helps you identify blind spots, biases, and oversimplifications in your thinking.

More specifically, counterevidence thinking is suited for answering questions like: Is what I’m seeing a fact, an assumption, or a habitual practice? To make a better choice, which variable, which path, or which constraint should I examine first?

When to Use

• When the problem becomes complex and intuitive judgment is less reliable.
• When the team disagrees on the next steps and needs a shared analytical framework.
• When you need to turn abstract judgments into concrete actions, checklists, or experiments.
• When existing practices are losing effectiveness and you need to re-examine the underlying logic.

When Not to Use

• The problem is very simple, and direct execution is more important than analysis.
• Basic facts are lacking, and you are just spinning in conceptual circles.
• The model is only used to justify an existing conclusion, not to help correct judgment.
• The cost is extremely high, trial and error is impossible, and there are no additional verification methods.

Steps to Use

1. Write down the current problem: Describe in one sentence what you need to judge or resolve.
2. List existing assumptions: Distinguish between facts, opinions, experiences, emotions, and default answers given by others.
3. Identify key variables: Find the 1-3 factors that most influence the outcome.
4. Form actionable options: Propose several different approaches based on the key variables.
5. Define the minimum validation: Use a low-cost action to verify which judgment is closer to reality.

Small Case Study

Suppose a team finds that new user conversion rates are declining. Using “counterevidence thinking,” instead of immediately asking designers to change the button or asking operations to increase the budget, they first break it down: Where do users come from? What information do they see? At which step do they hesitate? What do they lose when they abandon? Are there stronger alternatives? After breaking it down, the team may discover that the real problem is not insufficient traffic, but that users don’t understand what problem the product solves on the first screen. Therefore, the minimum action is not to redo the entire product, but first test a clearer value proposition.

Dissipative Structure Theory

One-Line Definition

An open system far from equilibrium can spontaneously form higher-level ordered structures by exchanging energy with the outside world.

Core Concept

Prigogine’s dissipative structure theory: an open system, when far from equilibrium, can form new, higher-level ordered structures by exchanging matter and energy with the outside world.

What Problems It Solves

When information is incomplete, options are numerous, or risks are unclear, it helps pull your judgment back from intuition to structured analysis.

Double Goal List

Definition in One Sentence

List 25 goals you want to achieve, circle the 5 most important ones — the remaining 20 are a list of ’things to avoid at all costs.'

Core Concept

Allegedly a method by Warren Buffett: list 25 goals → circle the 5 most important → the remaining 20 are not ‘do later,’ but ’never touch,’ because they will distract you from your top 5 goals.

Dunning-Kruger Effect

One-sentence Definition

Incompetent individuals tend to overestimate themselves, while competent individuals tend to underestimate themselves.

Core Concept

The Dunning-Kruger effect reveals a paradox of cognitive bias: the more ignorant, the more confident; the more expert, the more humble. This is because the ignorant lack the ability to assess their own competence.

What Problem Does It Solve

When information is incomplete, options are numerous, or risks are unclear, it helps pull your judgment from intuition back to structured analysis.

Dynamic Thinking

One-Sentence Definition

Recognize that things are constantly changing, and view problems with a developmental perspective.

Core Concept

Dynamic thinking requires us to see problems from a changing and evolving perspective, rather than treating the current state as fixed. Today’s optimal solution may be tomorrow’s pitfall.

What Problem Does It Solve

When information is incomplete, options are many, or risks are unclear, it helps pull your judgment from intuition back to structured analysis.

Efficiency Thinking

One-Line Definition

Maximize output with minimal resource input.

Core Concept

Efficiency thinking focuses on the input-output ratio, aiming to create more value with less time, energy, and resources. However, efficiency is not the same as effectiveness—doing the right things is more important than doing things right.

What Problem Does It Solve?

When information is incomplete, options are many, or risks are unclear, it helps pull your judgment from intuition back to structured analysis.

Eisenhower Matrix

One-Sentence Definition

Use the two dimensions of importance and urgency to differentiate how tasks are handled.

What Problem Does It Solve

When resources are limited and tasks are numerous, it helps you identify the key actions that truly impact results.

More specifically, the Eisenhower Matrix is suited for answering questions like: Is what I’m seeing a fact, an assumption, or a habitual practice? If I need to make a better choice, which variable, path, or constraint should I examine first?

Expected Value: Thinking in Long-Term Averages

One-Sentence Definition

Expected value is a probability-based decision model that multiplies each possible outcome by its probability and sums the results to estimate the long-term average result of a choice.

TL;DR

• Expected value helps you evaluate choices by weighing both probability and payoff.
• It is useful when a decision involves uncertainty, trade-offs, or repeated bets.
• A positive expected value does not guarantee a win in one attempt; it means the choice is favorable over many repetitions.
• The main risk is ignoring worst-case downside, even when the average outcome looks attractive.

What Problem Does It Solve?

Expected value solves the problem of judging decisions only by single outcomes. A good decision can fail once, and a bad decision can succeed once. Expected value shifts attention from short-term luck to long-term probability advantage.

Fake Door Test

One-Sentence Definition

A Fake Door Test measures user interest by presenting a realistic entry point for something that is not fully available yet.

TL;DR

• A Fake Door Test measures user interest by presenting a realistic entry point for something that is not fully available yet.
• Use it to make judgment more concrete and less reactive.
• Apply it with clear evidence, boundaries, and next actions.

What Problem Does It Solve?

Fake Door Tests solve the problem of building from opinions instead of behavior. A fake door places an offer in a realistic user path and checks whether users actually try to use it before the team pays the full build cost.

Feedback Loops: How Results Shape Their Own Causes

One-Sentence Definition

A feedback loop is a causal cycle in which the result of a system affects the conditions that produced it, creating either self-reinforcing growth or self-correcting stability.

TL;DR

• Feedback loops explain why some systems accelerate while others stabilize.
• Positive feedback amplifies change; negative feedback dampens change.
• They are useful for understanding growth, decline, habits, organizations, and complex systems.
• The key is to identify what output flows back into the system as a new input.

What Problem Does It Solve?

Feedback loops solve the problem of thinking in simple one-way cause and effect. Many outcomes are not produced by a single action, but by repeated cycles where results change the next round of behavior.

Fermat-Pascal Thinking

One-Line Definition

Use probability and expected value to evaluate decisions, making judgment more rational.

Core Concept

Fermat and Pascal pioneered probability theory. The core idea: when facing uncertainty, multiply probability by gain/loss to calculate expected value, and choose the option with the highest expected value.

What Problem It Solves

When information is incomplete, options are many, or risks are unclear, it helps pull your judgment away from intuition and toward structured analysis.

Feynman Technique

One-Line Definition

Explain complex concepts in the simplest language — if you can’t explain it clearly, you haven’t truly understood it.

Core Concept

The Feynman Learning Technique consists of four steps: Choose a concept → Try to teach it to someone else in simple language → Identify where you get stuck → Go back to the original material and re-learn → Simplify your explanation.

What Problems It Solves

When information is incomplete, options are numerous, or risks are unclear, it helps pull your judgment from intuition back to structured analysis. More specifically, the Feynman Technique is suitable for answering questions like: How can I better understand the current situation? How can I make more reasonable judgments and take action?

First Principles Thinking: Rebuild Solutions from Fundamental Facts

One-Sentence Definition

First principles thinking is a mental model for breaking a problem down to its most basic verified facts, then reasoning upward to build a solution from the ground up.

TL;DR

• First principles thinking separates facts from assumptions, habits, and inherited industry beliefs.
• It is useful when existing solutions feel too expensive, slow, complex, or outdated.
• The goal is not to sound deep; the goal is to produce a better, testable solution.
• It is powerful but costly, so do not use it for every simple decision.

What Problem Does It Solve?

Many bad decisions come from treating assumptions as facts. Teams say things like, “customers will never do that,” “this is how the industry works,” or “this kind of product must be expensive.” Some of those statements may be true. Many are just inherited beliefs.

Five Whys: Do Not Stop at the First Reasonable Cause

One-Sentence Definition

The Five Whys is a root-cause analysis method that asks “why” repeatedly to move from surface symptoms toward deeper causes that can be acted on.

TL;DR

• The Five Whys helps you move beyond symptoms and identify deeper causes.
• The method is simple: state the problem, ask why, then ask why again for each answer.
• It works best when answers are grounded in facts, not guesses or blame.
• It is useful for recurring problems, process failures, product issues, and team retrospectives.

What Problem Does It Solve?

The Five Whys solves the problem of fixing symptoms instead of causes. Many teams stop at the first plausible explanation, make a quick fix, and then see the same issue return. Repeated “why” questions push the analysis deeper.

Flow State

One-Line Definition

A state of heightened focus and immersion when challenge and skill are matched.

Core Concept

Psychologist Mihaly Csikszentmihalyi proposed that flow is a state of deep focus that emerges when skills and challenges are balanced. When it is too easy, boredom sets in; when it is too hard, anxiety takes over.

What Problems It Solves

When resources are limited and tasks are many, it helps you identify the key actions that truly drive outcomes.