First Principles Thinking

How it works

Most reasoning is by analogy: “This is how it’s always been done” or “Company X did it this way, so we should too.” Analogy is efficient but it inherits all the assumptions and limitations of whatever you’re copying.

First principles thinking takes the opposite approach. You decompose a problem into its most basic elements — the things that are undeniably true — and then reassemble your understanding from scratch.

The process follows three phases. First, identify your assumptions about the problem. Write down everything you believe to be true about the situation. Second, challenge every assumption by asking “Is this actually true, or is this just convention?” Strip away anything that isn’t a fundamental truth. Third, rebuild from the ground up using only the truths that survived your challenge.

Case study: How Elon Musk cut rocket costs by 90%

In 2002, Elon Musk wanted to buy a rocket to send a small payload to Mars. NASA quoted prices around $65 million per launch. Russian vendors wanted $18 million — for used ICBMs. Instead of accepting the market price, Musk asked: “What are rockets actually made of?”

He broke a rocket into its raw materials: aerospace-grade aluminium alloys, titanium, copper, carbon fibre composites. He priced each on commodity markets. The total material cost was roughly 2% of the purchase price. The 50x markup came from decades of inherited manufacturing processes, cost-plus government contracts, and an industry with no incentive to innovate.

SpaceX built its own rockets from materials up, vertically integrating manufacturing. By 2020, a Falcon 9 launch cost under $3 million. Musk didn’t negotiate a better price. He decomposed the problem and rebuilt from fundamental truths.

Real-world examples

SpaceX rockets. The conventional wisdom said rockets cost $65 million because “that’s what aerospace companies charge.” Elon Musk broke the rocket into raw materials — aerospace-grade aluminium, titanium, copper, carbon fibre. The raw material cost was roughly 2% of the typical price. The question became: “Why is there a 50x markup?” The answer was inefficient manufacturing processes inherited from decades of tradition. By rebuilding from material costs upward, SpaceX reduced launch costs by a factor of 10.

Education. The assumption: “Learning requires a classroom, a teacher, and a fixed schedule.” The fundamental truths: learning requires information, practice, and feedback. From these truths, you can build entirely different systems — spaced repetition apps, project-based learning, peer teaching — that may work better than the conventional model for many learners.

When to use it

First principles thinking is most valuable when working in an established field where “best practices” may actually be outdated habits, when you’re trying to innovate rather than incrementally improve, when cost reduction is the goal and you want to understand what you’re actually paying for, and when expert advice conflicts and you need to reason from ground truth.

Common mistakes

The biggest pitfall is using first principles thinking for everything. It’s computationally expensive — it takes real time and energy. For routine decisions, reasoning by analogy is faster and good enough. Reserve first principles for the decisions that matter most. The second mistake is confusing “I haven’t heard this before” with “this isn’t true.” Conventional wisdom exists for a reason. Sometimes the established approach really is correct.

Try it now

Pick something you believe to be expensive, slow, or impossible. Write down every assumption about why. For each assumption, ask: “Do I know this is true from direct evidence, or am I repeating what I’ve heard?” Cross out anything that fails this test. What remains?

Related models

These models complement First Principles Thinking — they address similar situations from different angles.