There are also people who unintentionally take on traits of the people they're surrounded by most. If particularly empathic they'll even think or feel things that aren't their own originations. Obviously, this would be confounding to a person observing them.

Some people (usually the more rigid types) like to think that a person has to be set in habits and personality. They like a person to match their estimation of them and get upset when the person doesn't line up. How dare they not line up with their expectations! Lol. The thing is, some people's set quality is one of being changeable. They won't ever be the same from one moment to the next, that is who they are. A chameleon, if you will.