First Principles Thinking is the practice of breaking down a problem to its most fundamental truths — the facts that cannot be reduced further — and building your understanding from there.
Instead of reasoning by analogy (doing something because others do it), you strip away assumptions and start from what is actually true.
This method was used by Aristotle, applied by Elon Musk to reinvent rocket manufacturing, and is one of the most powerful cognitive tools available to a strategic thinker.