Expert judgement is a human decision based on experience and context when a rule cannot be fully automated. Security controls may require interpretation because systems, risks, and operating conditions differ. A reviewer might use professional knowledge to decide whether a control is effective in a particular environment.
In cyber security, this judgement can help address situations a checklist cannot capture, but unclear criteria can make results inconsistent. Different assessors may reach different conclusions about similar systems, weakening confidence in an assurance or compliance review. Organizations can improve repeatability by defining assessor qualifications, documenting decision criteria, recording evidence and rationale, and using peer review for important findings.