What is the MOST important reason to configure unique user IDs?

Unique user IDs are essential for supporting accountability, which is the ability to trace actions or events to their source. Accountability is a key principle of security and helps to deter, detect, and correct unauthorized or malicious activities. Without unique user IDs, it would be difficult or impossible to identify who performed what action on a system or network. Reducing authentication errors, preventing password compromise, and supporting Single Sign On (SSO) are all possible benefits of using unique user IDs, but they are not the most important reason for configuring them. References: CISSP All-in-One Exam Guide, Eighth Edition, Chapter 1, Security and Risk Management, page 25. Official (ISC)2 CISSP CBK Reference, Fifth Edition, Chapter 1, Security and Risk Management, page 38.