Truth is... people just do not fit that well into a box. They are dynamic, complex, and ever-changing. They have different aspects of themselves that they draw on at different times.
To get to know someone, we have to be open to who they are all the time. We have to put away our preconceptions of them and pay attention to who they are right now. We may be witnessing the first time they ever exposed that part of themselves to someone.
But most folks do not go to all that trouble. Much easier to make assumptions about people. Then we do not have to think about who this person is. We do not have to continually redefine and discover who they. Most of all, we do not have to redefine who we are in relation to them. We do not have to feel or get involved. That could be risky and downright uncomfortable.
Plus that way we can create the illusion that we can control them. Much safer that way.
Only problem is... we miss our once-in-a-lifetime opportunity to discover who that person really is in this moment. We fail to see how their beauty is beyond definition.