I think it depends on the context: where/when, for how long, etc. I recall an older woman I'd known as an acquaintance for years who seemed so happy and full of life whenever I saw her. Bubbly. One day I was still sitting in my car and she didn't realize anyone was around as she walked into view, and all of the happiness and effervescence had melted away. Her face showed emotional pain, misery even. It was obvious to me in that moment that she was a deeply unhappy person but she put on the pretense of joy for the sake of others, to not let on to anyone that she was deeply discontented. So, I'd agree that you can learn a lot about someone's personality through observation, but it may be hidden, it may take time, and it may not show unless you happen to see them with their guard down.

Have someone. video you without your knowledge and see how much you can learn about yourself seeing your own interactions with people from an outside viewpoint.

I think you could learn everything about someone without ever having to interact with them at all. Of course, this would require a great deal of time and effort, and probably some illegal activity.

That's a well of thoughts. I'm more inclined, as a major people watcher from being the quiet type in gatherings of all aspects, that I've learned more about myself than those I watch. I might even go as far as to consider it a study of society over people watch? Outside of how I've used this to develop my own character and opinion on society, I can only place a personal opinion on a personality towards someone I actually know, or getting to know. I hate crowds. I really do not enjoy getting out into society much at all. But as I sit among as I must at times, it provides a well of entertainment, enlightenment, fears, and hope.

I use this power (its one of my superpowers! shhh) all the time whenever I feel the urge to go to tinder....

I also love turning the volume on a TV to zero, and just watch it without sound, you see a great deal and hear a great deal that you didnt notice before!

I believe you learn more about YOURSELF when "observing" others. If YOU are looking at another and labeling that person with whatever attributes that your filter allows you to use is rather insightful, if you are honest with yourself.

You can tell a lot about a person from the way they treat other people, animals or even what they do when they think no ones looking. If you are in a crowded bar and somebody goes to get another drink and leaves the empty sitting at the table, pushes through people without so much as a by you leave and is quite determined to get served first even though there are other people who were there before them, you can be fairly sure they are a selfish jerk.
Once was having a drink with a man at their home and their dog was there. It's coat was full of matted lumps so as I'm sitting there drinking a glass of wine I am gently teasing the matted lumps out of its coat. He notices and guesses what is running through my mind and says "Oh, this is amazing because the dog won't let him groom it". Anyway sent him to get some shopping bags and filled three of them with matted fur before I left. Needless to say never went back, if a guys own dog won't trust them but will trust a complete stranger I don't want anything to do with them.

How secure, or insecure they are. You can see thru the weak, and that does not require any form of judgement. Their posture, stance, and mannerisms allow you to see their fears

Yes. You can sense a lot just by where they are looking. Can I take a peek?

eyes tell the world the truth

I don't know but anyone who has time to observe that much needs a new hobby. Or a job.

I'm certain that we take in a lot of information subliminally from a person's body language and especially facial cues. I definitely know sometimes when something is "off" as soon as I meet a person, by eye movements and probably from their pupils and irises and detectable movements of the muscles around the eyes. Often we discount the hunches these subliminal clues give us, and sometimes at our peril. One thing that makes it difficult to trust our hunches is that many of us have intrinsic and often unconscious attitudes toward particular body types that, although not valid, give us similar kinds of feelings to the ones we get from the subliminal cues.

I have certain criteria that I have used in my 79 years which has been pretty accurate. The first is their manner of dress,next hygene finally the use of their language skills relative to their education levels.A slob in dress generally attests to a slob in all other matters as do the other two. It is a very simple test but is very accurate.Next is how they treat others and animals especilly those who it can be seen are less strong. slobs like to take advantage of those they preceive weaker than themselves.A person does not need an advanced degree to be a very nice person.I have a freind who did not finish school but he is obe of the kindest most gentle person even though hr is about 6'6 ' over 300 lbs.

I have a habit of not looking at people when listening to them or talking to them. Seemingly many are uncomfortable with this and it explains why I so much prefer to talk with people on the phone rather than face to face. The main reason is that I so frequently see the incongruity between people's body language and their spoken words. My ears are also unusually sensitive to the sound of peoples voices and unfortunately it seems that many these days do not realise how lifeless or untruthful theirs are.

Until about age 18 I was severely shy and undersocialized so I never knew when to speak in a group larger than 2 persons. As a result, I didn't speak--I oberserved. I'm a naturally curious, observant person anyway; I learned so much this way. I didn't even realize until much later--when I finally started talking to people--how much of a leg up I have on the average Joe when it comes to reading people.

It's so innate and subconscious I don't even think I can put it into words. I'm too scientific to ever forget that I could make an error at any time, but I have very high confidence in my ability to interpret facial expressions, determine motivation, measure enthusiasm or confidence, spot a liar, etc. Moreover, I don't think it takes a genius to make certain inferences about the way a person thinks and some of their attitudes by how they do or do not answer questions or develop a conversation.

Basically, because I grew up never being preoccupied by what I had to say, I had plenty of time and room in my head to read between the lines. In a way, everything was reading between the lines. It became second nature to me. Most people strike me as fairly transparent. Manipulators, liars, and game-players freak me out badly, because their ruses are glaringly obvious.

Whether or not they are congruent.
Whether or not they have and use a brain.
Whether or not they are kind.
Plus a million other mundane characteristics.

Body language wardrobe posture gestures hair and cosmetics might signal social attitudes and a few character traits bit people are defined by their principles = personality

It's interesting to notice that most of us observe without judgment about the behavior of others. I also like to watch and look for the story. The story always contains real human drama involving fears and happiness, signs of masked depression and secrets, anger and competition. There's no story without conflict. But it's interesting reading all the comments since my last comment this late morning how many of us enjoy watching and listening in order to better know the people we are with. I used to drive my children in carpool back and forth to school. If I asked them, "what did you do today at school?" I would get, "Oh nothing." But if I listened to the conversations of the kids as I drove them home, I learned what really happened at school. As I've finally learned more and more to shut up and listen to my loved ones and friends, I've known them better and argued with them much less than before.

I love to watch people. Any city less densely populated than NYC is too few people for me. Even though I believe I can observe many things that turn out to be true of others, I always keep in mind that I'm making assumptions based on my own experiences and I'm often wrong, I like to overhear conversations in restaurants and on the streets, people talking on their cell phones. Little bits of other people's lives combine to make interesting stories of fiction. Real life, the way people really talk and relate to each other is fascinating. Of course, I have my own intimates as well. But the world is full of people and situations that are being negotiated at all times. I also love politics. It fascinates me too.

It all depends. Some people are good at observing people and reading gestures, body language, etc... Some people want to be good at that but they are not necessarily. Anyway by the way they walk you could have an idea of how insecure this person is when they talk you can have an idea if the person is a liar. You can have an idea of vow this person was raised... Of course there's nothing absolute but at least an idea.

Depends on the person. I can generally figure out a person within 20- 30 minutes including their past but i took criminal psychology and profiling. You can usually tell if someone is really happy or just putting on a show or if the person is "damaged"

My wife is quite intuitively insightful about people and is usually right in what she deduces from what she observes. Far more often than I am. To the point that I generally / provisionally rely on this ability of hers.

But boy, when she's wrong, she's spectacularly wrong.

So I don't think we should take our observations so seriously that we think them infallible. Because science has demonstrated that people tend to make snap judgments based on first impressions and then are fiendishly reluctant to revise those judgments even in the face of overwhelming contrary evidence later.

I am rather sensitive to inaccurate snap judgments others make about me and notice it happens with some regularity. Sometimes it can cut short attempts at new relationships or associations. Not just to me, but to others. My wife for example was a new volunteer with a charity and was super impressed with the person in charge, who treated everyone, including her, very respectfully and well. Suddenly one day this person wouldn't give my wife the time of day, despite displaying the same openness to others. It left her wondering what she had done to offend the woman. It was quite a striking change. And in the face of that you kind of wonder if it's worth the confrontation to even figure it out, if people are that brittle and arbitrary with their snap judgments.

You can learn a lot about people. In past I learned things about co works just by observing them, Then I like to when they say...I always reply I figured that out about..ago...

Look for the Cues of their Lies