First Principles Thinking
Deconstruct a problem to its core components, then rebuild instead of copying the past
- Difficulty
- Moderate
- Time to result
- ~weeks to results
- Steps
- 5
- Confidence
- 88%
First principles thinking, drawn from physics and popularised by Elon Musk, deconstructs something to its irreducible parts so it can be reconstructed from scratch. Its opposite is reasoning from analogy — assuming a thing must cost or work as it always has because that is how it was done before. Musk's battery example: rather than accept that a battery pack costs a fixed amount, he broke it into raw materials, priced each on the metal exchange, and found a fraction of the cost, leaving only the problem of reassembly. The method applies beyond engineering: MacGill uses it to interrogate why school starts at 9am, to strip his own life down to time and energy, and to reassess relationships by asking what their component parts should actually be.
Origin
MacGill traces first principles to physics, popularised by Elon Musk on the Joe Rogan podcast. He contrasts it with 'reasoning from analogy' and cites Musk's SpaceX battery cost breakdown and Daniel Gross's questioning of school start times.
Core principles
- 01Reasoning by analogy is copy-paste thinking
- 02Everything can be reduced to core components
- 03Rebuilding from fundamentals reveals hidden cost and possibility
- 04Question inherited assumptions rather than accepting the old guard
How to run it
- 1
Pick the target
Choose the object, cost, or convention you want to rethink — a product, a schedule, or a life decision.
- 2
Spot the analogy trap
Identify where you are assuming something must be a certain way because it has always been that way.
Pro tip Reasoning from analogy feels like knowledge but is just copy-paste.
- 3
Break it into components
Decompose the thing into its fundamental parts or the underlying reasons behind a decision.
Pro tip Write every reason or ingredient down, as Paul Graham advises, before judging it.
- 4
Assess each part on its own
Price, test, or validate each component independently of the whole.
Watch out Don't stop at the first component; the insight usually hides in the full breakdown.
- 5
Reconstruct from the ground up
Reassemble a solution from the validated parts rather than the inherited default.
In the wild
Told that a battery pack simply costs a fixed high price because it always has, Musk broke it into raw materials — lithium and the other constituents — and priced them on the London Metal Exchange, finding roughly a tenth of the quoted cost. The remaining problem was simply finding a cost-effective way to reassemble the ingredients into a battery, turning an accepted price ceiling into an engineering challenge.
→ A supposedly fixed cost collapsed to a fraction once rebuilt from fundamentals.
Isolated on holiday in Gran Canaria, MacGill tried to break his life down to first principles and concluded the only things that truly matter are time and energy. Every subsequent decision became a filter: will this give me more time or more energy? This replaced a head full of borrowed analogies about how he 'should' be living.
→ A single two-variable decision filter replacing anxious social comparison.
Common mistakes
Reasoning from analogy in disguise
Copying the previous version with cosmetic tweaks feels like thinking but just inherits old assumptions.
Halting the breakdown too early
Stopping before you reach genuinely fundamental components leaves the real assumption untouched.
Is it for you?
Best for
Redesigning systems, cutting costs, or rethinking a situation everyone else copies from the past.
Not ideal for
Fast routine decisions where established convention is already near-optimal.
From the transcript
“reason from analogy so they just read them from the way it's been before and just copy and paste”
“he goes okay how much would this cost to buy off the london metal exchange and it comes down to like a tenth of the…”
From the episode
Mental Models 101 - How To Make Better Decisions - George MacGill - #069
George MacGill