Security principles: least privilege, role-based access, CIA triad, defense in depth, zero trust, segmentation

Security principles are the ideas behind every specific control. Firewalls, VLANs, MFA and encryption are tools; principles tell you why and where to use them. When an exam question describes a situation and asks which principle applies, or which design is best, these concepts are what it is testing. They also help in real work, because when you face an unfamiliar product or situation, you can still reason about it from the principles.