Why do we naturally see the need to read people?

Why would anyone want to learn the art of reading people like a book? That concept in of itself is often romanticized as a gift, a talent that gives you an advantage in social interactions.
We have to be honest, people have always observed one another. Before anyone ever uttered the word psychology, people were already noting tone, reading silences, monitoring subtle shifts in behavior. It's more of a survival instincts because a snake and a lion are not the only threats people are concerned about, we know all too well from history that your fellow can be an even bigger threat.
Words alone were never enough to figure someone out, predict their next move and decide your next move as well. And words still are not enough. A lot of the times, people say things they mean only half of, or they say nothing at all, so we fill in the blanks.
I once found myself in a mini bus, eavesdropping on the conversation of two friends. One was smiling, but I realized his posture was a bit rigid, almost clenched. I kept thinking to myself, this smile is doing too much. It later came out that they had gotten into a fight the previous night. Perhaps I knew it perhaps I merely assumed it, it's hard to tell.
On a different occasion, I believed someone’s words because they sounded so rational and liars can lie with such precision and calmness these days. Everything was okay, they assured me. Except weeks later it became patently clear that everything was most definitely not okay. I like I had somehow missed the obvious. After that incident, I began to observe people a bit more.
I think this instinct to try to read before usually stems from hurt. When your trust is violated, you begin to look for signs of more deception everywhere, patterns and discrepancies. You tell yourself you are being cautious and sometimes it's true but perhaps you are simply tired of being blind sided.
Modern life hardly helps. Things move so fast from jobs to friendships and especially intimacy. You are expected to somehow know people so quickly. So you observe, you try to read them, then you make the mistake of over reading.
The issue is less about reading people and more about assuming we have finished the book. Books have endings, human beings don't.
https://www.reddit.com/r/coolguides/comments/1qauect/a_cool_guide_to_read_a_person_like_a_book/
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