There are tons of things a person wouldn't be able to tell about me the first time they met me. All they would see is a surface, a cover up of who I really am. No one would ever know what I'm actually made of inside just by looking at me. It's very easy for me to cover up what I'm feeling. I'd consider myself a pro at being emotionless, although I do in fact have emotions. There are multiple aspects to my identity that people who actually "know" me today, still don't even know. I'll state some of these aspects below.
One aspect one wouldn't be able to see by looking at me is how friendly and outgoing I actually am. Generally, I'm a very quiet and shy person. The first time we meet, the most I'll ever say to you is "Hi" or Hello". People call me really shy, but it's only because I don't really know them. I need to first observe what kind of person you are before I actually engage in a conversation. It takes a while for me, but once I'm used to you... BAM! Once I see that I'm getting used to you, it's as if I never stop talking. I can sometimes be really annoying. Once people see how much I actually talk, they sometimes forget how "shy" I once was.
Another aspect one wouldn't be able to see by looking at me is how emotional/dramatic I am. The way I portray myself to most people (that I don't know), is that I have no emotion. The tone of voice I speak in, the way I blankly look at people, the way I react to certain situations... it makes people think that I'm really emotionless. But I in fact do have emotion. It takes a while for people to see that in me because I don't express it the first time I see someone. It takes time, lots of time. It also depends on how well I know you, if I know you very well I get very emotional around you. Like most situations, I have to observe the person. I have to understand what kind of person you are in order to open up and show emotions towards them.