The people-management tag didn't have a wiki so I drafted one based on my understanding of the questions.
This probably deserves some attention right now, so I'm posting my draft in the hope that it can be greatly improved upon.
People matter to security from employees who are targets of social engineering, to architects & engineers who devise and implement security-critical policies. People management involves preventing these people from becoming part of an attack by filtering out bad actors (e.g. background checks), helping good actors act well (e.g. education), and, and preventing single points of failure (e.g. limits on intra-departmental communication).