I mastered the art of blank face in my early teens.
My mother helped me with this process. For various reasons of her own, she offered inconsistent comfort and discussion. An example: One day she said I could get a cat. I said no because I didn't want to be any trouble for her, and in my family, having my own opinion about something seemed to me to be quite a bit of trouble for everyone else. I later realized that I did actually want that cat. When I returned to my mother to ask for the cat, her face acquired a smug look and she chortled, "No."
At the time, I didn't know how to address conflict. My current self would say, "You're offering information that's inconsistent. A few months ago, you said I could get one." Younger me didn't believe in my own strength. Younger me wasn't aware of strength except as displayed in other people, particularly my parents and older siblings.
I can offer all manner of explanations that would make my mother appear as a saint. Many people see my mom as a harmless creature. And in the biggest scheme of things (on a spiritual level), she is indeed harmless. She tried her best. She did what she could. All that.
In my earlier relationship with her, I needed to develop blank face in order to survive. I couldn't let her know that she had hurt me. That would be giving her some kind of power. The only way she would know is if I told her through my words or the look on my face. To keep my own sense of power in place, I maintained blank.
This worked for a time.
Then it started to be more of a problem than a solution.
As you may have noticed, people often like to define blank. I started to notice alarming statements from others. They would speak. I would consider their words in my mind. I would decide that I needed to give it more consideration. Or I'd decide that the person was _something_ and I needed to _something_, and then I'd keep those decisions in my mind because I didn't want to hurt someone else's feelings (which is what I might do if I displayed disagreement); or I didn't want to inconvenience anyone; or I didn't want to take up more space than absolutely necessary. My almost entirely internal dialogue encouraged questions from other people.
There I was, totally engaged in what the other person was saying or how what they were saying affected other topics, and the other person didn't know if I was even present for the conversation! That scared me. What was wrong with me? Why did this person not get me? Why couldn't s/he understand me? There must be something faulty in my brain, I acknowledged -- privately, of course.
I write about this as if it all happened in a straight line. The truth is, there were many circles and straight lines and other manifestations of paths that got me to today.
I can see now how words and facial expressions help other people understand where people are at with conversations. Now I value interaction with others and will try to explain that I'm thinking or that the reason I'm looking away is so that I can visualize what the person is saying. If provided information is different from previous data, I point it out and may ask why. If I don't like the answer, I say so. If the new arrangement isn't acceptable, I make necessary changes in my life.
Sometimes I still utilize blank face. I like it as an assessment of another person's current mental station. Does s/he try to explain a lot of details to me -- details for which I didn't ask? Then it's possible that s/he feels insecure. (Adding unrequested details can be a way for someone to say, Hey, I'm important. Look at all of this stuff I know. Acknowledge my worth.) I can plan my words accordingly. Does s/he flare into anger or impatience because I display confusion? Maybe I need to separate from this interaction or perhaps address it directly [I sense impatience. I don't understand what you just said. It will help me if you can say this in a patient manner.] Or perhaps the other person is feeling fear.
I used blank face with that coworker who attempted to intimidate me. When I declined his attempt to escalate the situation, I kept blank on my face as I said no. As it turns out, he thought I was attacking him. Apparently, he stood up because his interpretation was that my voice increased in decibel as I said, "Really?" In this case, blank face showed me his anger. Later, I learned that fear was under his anger. Did his feeling of fear justify standing up in my face? To him, it did. To me, it didn't. So, blank face has its utility. So do other tools, such as conversation.
Well hello there.