By 6days · v1.0 · Updated 7/20/2026
Strip a problem back to what must be true, then rebuild — instead of copying what exists.
Fill this in for your own situation — a private worksheet only you can see.
When to use
Use it when an industry's costs or practices have been stable for a long time without obvious justification, when you are entering a field as an outsider and lack the incumbents' assumptions, or when repeated incremental attempts have all failed and the problem may be framed wrongly.
When not to use
Avoid it for routine decisions — it is slow, effortful, and analogy is right most of the time. It is also a common vehicle for arrogance: reasoning from first principles while lacking domain knowledge tends to rediscover why the convention exists, expensively. If experts cannot explain why a practice exists, that is worth investigating; if they can, listen.
Most reasoning is analogy: we do it this way because that is how it is done, because the incumbent does it, because we did it last time. Analogy is efficient and usually right, which is exactly why it is dangerous — it carries forward constraints that were real once and quietly expired. Whole industries hold assumptions nobody has tested in decades, because testing them was never anyone's job.
First-principles thinking decomposes a problem to the things that must be true — physics, arithmetic, contract terms, hard constraints — and reasons upward from there, deliberately ignoring how the problem is currently solved. The hard part is not the rebuilding; it is telling a real constraint from an inherited convention. 'Water boils at 100°C at sea level' is a principle. 'Enterprise software is sold through channel partners' is a convention wearing a principle's clothing. The method is expensive and usually unnecessary — its value is concentrated in the rare cases where a load-bearing assumption is simply wrong.
Framework by 6days on 6days — https://6days.apexaion.ai/framework/first-principles-thinking
Write the problem so that no current approach is embedded in the wording. 'How do we make our call centre more efficient' has assumed a call centre. 'How do customers get their question answered' has not, and the two questions have very different answer sets.
Write down everything you believe about the problem, especially what feels too obvious to state. The load-bearing assumptions are always the ones nobody thought worth writing down, because obviousness is what protects them from scrutiny.
For each, ask what would happen if it were false, and demand evidence for why it holds. Laws of physics, arithmetic, and binding contracts survive. Industry practice, precedent, and 'the customer expects it' usually turn out to be conventions that someone chose, under conditions that may no longer apply.
Construct a solution using nothing but the constraints that survived. Do not check it against the existing approach yet — the comparison will pull you back toward the familiar before the new idea has finished forming.
Set the rebuilt solution against the status quo. Often the status quo wins, which is a real and useful result: you now know why it is right rather than merely inheriting it. Occasionally the gap is enormous, and that is what the whole exercise was for.
Worked example
A team is quoted £40,000 for a piece of lab equipment and treats it as fixed. Decomposed: what is it actually made of? A precision stage, a camera, a light source, a controller, an enclosure, and software. Priced as components, roughly £6,000. The remaining £34,000 is not physics — it is certification, low production volume, support, and margin, all of which are real costs but not laws. For a regulated clinical setting the £40,000 is justified and the analysis ends there. For an internal research rig that needs no certification, most of that gap is avoidable, and the team builds it for £9,000.
The idea is ancient: Aristotle described reasoning from first principles, and the method underpins mathematics and physics as disciplines. Its modern circulation in business owes much to engineering culture and to founders who have publicly credited it for cost-structure decisions. It is common intellectual heritage rather than anyone's proprietary framework.
Related ways to think about this.
Ask how this fails, not how it succeeds — the failure list is shorter and more honest.
Use when Use it before committing to a plan that is expensive to reverse, when a team has become uniformly enthusiastic and you suspect the optimism is social rather than evidential, and in any decision where avoiding a catastrophic downside matters more than optimising the upside.
Avoid when Avoid it as a general operating posture — a culture that only inverts becomes paralysed and treats every idea as a hazard. It is weaker in genuinely novel territory where the failure modes are unknown rather than unspoken. And it will not generate a strategy: it removes ways to lose, which is not the same as finding a way to win.
Observe, orient, decide, act — and win by cycling faster than the situation changes.
Use when Use it in genuinely competitive, fast-changing situations — an incident, a live negotiation, a competitor's surprise move, a crisis. It suits environments where information is incomplete by nature and waiting for completeness means losing.
Avoid when Avoid it for decisions that are expensive to reverse and slow-moving: a factory site or a pension scheme does not want tempo, it wants analysis. It is widely misread as 'decide fast', which drops the orient step and produces speed without judgement. It also has little to say where there is no adversary and no clock.
Separate urgent from important, and notice how much of your week serves neither.
Use when Use it when you are busy but not progressing, when a team is permanently reactive, or during a periodic review of where a role's time actually goes. It works well as a recurring habit rather than a one-off, and it is a useful device for a manager and report to look at a workload together without it becoming personal.
Avoid when Avoid it where you have little real autonomy — telling someone to delegate work they cannot delegate is just a way of blaming them for their constraints. It handles individual tasks better than long collaborative efforts, and it has nothing to say about work that is important to someone else and not to you, which is most of what makes a job hard. It also assumes you can tell importance from urgency, which is exactly the skill people struggling with this tend to lack.