For example… I've been seeing the same orthodontist for over seven years, and I still can't find any difference between her and her assistant. Everytime I go see them, I make sure I notice all the small details. And fail miserably. Something like this seems to go through my head: Both of them are women. Both are Caucasian. Both have short hair dyed red. Both wear glasses and white clothes. What does that mean? They're the same person. It gets embarrassing when I need to talk to my doctor and don't know who she is.

When I was in middle school (11 - 15 years), there were two boys with whom I shared some classes, but I never saw them together with each other. Both had orange hair and freckles and their surnames started with the letters Ko. Because of that I spent four years thinking they were one person.
And it still happens to me. A lot. It took me two years to finally be able to tell my two classmates apart. And when I got to know them better, I realized that they don't look alike at all. But they're all the same unless I master their speech patterns, facial expressions, clothing style, and body language. But that takes time (and lots of uncomfortable situations in my case).
Do you know a way to make this stop? It's been driving me nuts.
