First principles is a method of solving problems by breaking them down to basic facts, rules, and constraints instead of copying an existing answer. In engineering, it means asking what must be true for a design to work, then building up from those fundamentals. This approach helps avoid assumptions that hide flaws.
In cybersecurity, first-principles thinking is useful for threat modeling, incident analysis, and secure design. Defenders use it to ask how authentication, trust, data flow, and permissions should work from the ground up, rather than relying on layers that only appear secure. Attackers can also exploit systems that were designed by assumption, finding weaknesses in interfaces, dependencies, or trust boundaries. The value of first principles is clarity: it helps teams explain why a control exists, how it can fail, and what must be protected if the system changes.