People
For practical purposes, "People" can be grouped into four categories: Self ("Me"), You, Us, and Them.
In the life experience, the relationship of people to the Self often shifts and changes.
Someone who is "Them" today may become "Us" tomorrow. Someone who was "Us" may become "You"—or even "Them."
This happens all the time. A stranger becomes a friend. A friend becomes a partner. A partner becomes an ex. A colleague becomes a collaborator. A collaborator becomes a competitor.
Category Shifts
Category shifts - or where any particular person fits on your map at any particular Time - generally have to do with alignment.
When you and another person share context, goals, or trust, you become "Us."
When that alignment breaks — through any of various means - a natural drift in a relationship, a divergence, or, perhaps at its most sensational, some form of betrayal: "Us" can become "Them."
Sometimes people who were on the same path just end up on different paths.
The Speed of Shifting
Moving from "Them" to "Us" tends to be a slow path. Trust builds gradually.
Moving from "Us" to "Them" can happen in an instant. Trust can erode quickly.