Day 5 · Act I — Lead Yourself

First-Principles Thinking

Assumptions · Root causes · Mental models

~30 minutes

Inherited answers are comfortable; examined ones are powerful.

The Core Idea

Organisations accumulate assumptions the way ships accumulate barnacles. 'We have always done it this way' quietly becomes a law of physics.

First-principles thinking strips a problem down to what is undeniably true, then rebuilds. It is slower than analogy — and that is the point. Use it for the few decisions where convention may be the constraint.

The Mental Model

The Five Whys

Ask 'why?' repeatedly until you reach a root cause rather than a symptom; associated with Toyota's production system.

At work: Customer churn rose → onboarding is slow → approvals queue → one approver → no delegation policy. The fix is a policy, not a discount.

The Case Study

Reusable rockets at SpaceX

DocumentedSpaceX developed the Falcon 9 with a reusable first stage, first landing one in December 2015.

Interpretation: questioning the assumption that rockets must be expendable reframed the economics of launch.

Cinema & Story

Apollo 13 (1995)

When the manual fails, reason from what is physically on the table.

The Reading Room

The Great Mental Models, Vol. 1

Shane Parrish

A practical toolkit of thinking models, including first principles and second-order thinking.

Further reading: Thinking, Fast and Slow — Daniel Kahneman

The Journal · Portfolio output: Assumption audit

1. Name one 'rule' in your team that nobody can justify.2. Apply five whys to a recurring problem. Where did you land?3. What would you build if you started this function from zero today?

The Field Experiment · within 24 hours

Bring one assumption to a team meeting and ask: 'What would have to be true for this to be wrong?'

The Evening Review

What did I learn?What did I do differently?What will I change tomorrow?

Question the floor before you build another storey.