I agree with the answer that people lie for many reasons. Some are pathological and most likely the cause or reasons that they get this way are probably varied as well. I worked for a woman once that was a nice person mostly. She worked very hard and was quite competent. She didn't have the appropriate education for her position and maybe that was related. I suspect she wanted to appear very good and competent and was not confident that her work or actions were displaying that. Example: when we were providing employee training and she was asked if provided a particular service......one that we really didn't.....she would answer it in a way that made it sound like we did. And she would always embellish what we actually did. In her case, her body language would give it away...to me, since I saw it over and over again. She seemed to stiffen and would turn her head back and forth very slowly and her voice would appear more monotoned than normal. Anyway, I can't stand liars. Once someone has lied to me, it's very difficult for me to trust that person at all. I understand a little white lie, but I'd rather not do that or have it done to me. That's like "do these pants make my butt look big".....I tend to tell the truth on those.

I think of your question within the context of game theory. Despite all the long winded and spurious reasons and explanations as to why people lie it simply reduces to one of two things. People lie because they are afraid to lose or they hope to make someone else lose. You are correct in paying attention to their actions. Einstein said: “If you want to understand the theoretical physicists do not pay attention to what they say but observe what they do.” His statement is not confined to physics and can be applied to all human interactions.

I try not to lie. I noticed that I had too much freaking fun and Luck to last a lifetime but I had been in situations where I was expected to lie. I love the phrase "If you tell the truth, you don't have to remember what you said". It is my motto. When I had an accident drunk in Germany while in the military. I didn't lied, I didn't allowed to be coached by my boss prior to make the statement to security. I gave my honest assessment. Only punishment was license suspended one year, that was it, to piss the hell of a lot of people. No reduction in Rate or nothing. I recognized that even people I never knew in the states begged for my leniency, based on having worked with my legally separated wife and knowing my character thru her. Then I was expected to be caught again driving without a license. During one year I never drove. Never caught drunk again. Regained my license but never did it again. I can tell stories that look more lie than truth because our expectations and how we think things should be. I had seen a woman walk into a club with her boyfriend and walk out with me. I had learned when you are after a woman never give up until she said No. Because you can't read minds. You can tell body language but is not a 100% science. And never take advantage of a drunk woman. I learned a new phrase this morning that I am planning to use for the rest of my life. Any woman dating me will be told "You have the right and obligation to remove Consent at any time you feel necessary". A relative once told me "To women you always tell them the truth but you don't have to tell them all the truth". We are victims of our actions. I don't want to be a victim of my lies. They say that too many details means a lie. I disagree but I had heard about body language of lie versus the truth. I call bluffs. And I had never played poker. When me and my wife got separated, she thought I was going to go to another woman, she expected that. She had on her mind I had a daughter with another woman just as she thought when she was my GF that I had a daughter with my previous GF. 18 years later she is planning her 3rd wedding. I only been married once, to her. No other children in my life. I had been lucky to last a lifetime telling the truth so why start lying now? I am also victim of my truths, mind you. So when she found a poem I dedicated to somebody else. I didn't lied about it. I accepted responsibility with all the Hell coming behind it. Truth Set Me Free.

Some people lie to be agreeable or to keep from hurting someone's feelings. Some lie about damn near everything, regardless of the weightiness of the matter because they are afraid of rejection or not fitting in. Some are just narcissistic shits that feel like anything that gets them what they want is justifiable. The one thing I learned when I was young was that people who are liars assume that everyone is a liar. I never was a liar and it was a jolt to me to find that I had been hoodwinked because of my own naivety. The problem with lying is that you no longer have any credibility with anyone once they are on to you.

they want there lives to seem more exciting or want something out of you I have found or just can't handle the truth.

Ask the orange one - a true Master of lies !

Well I am going to be very careful if I meet you someday. In fact I will not speak to you at all. LOL.
It's not that people believe truth or lie. I think it's more about how a thing is told to you. You need to connect with the other person. Also, people are comfortable living a lie if the truth is harsh and if it will rattle their system.. E.g. There are more religious people out there than atheist.

I think sometimes people lie because they are afraid the truth will get them in trouble or they lie to manipulate. Sometimes lying is part of a pattern of abusive behavior. I appreciate truth tellers and truth seekers and find them much easier to get along with.

I listen to a guy at work lie constantly. He lies about things he has absolutely nothing to gain from. It's his genetic makeup, and I really don't understand it. Granted, he's in sales and those phony mofo's can easily fall prey to the bad habit. But this guy lies or exaggerates with virtually every word out of his mouth. And he doesn't wash his hands after using the bathroom. I despise him. But he's always cool (fake) to me.

Well having a POTUS who is the biggest liar ever they strike me as very insecure people. They have no faith in themselves and hurt other people to feel better about themselves. Still their lies hurt people. trump's lies are going to harm the United States.

In physiology 101 one of the first thing that I had learned is that lying is a sign of intelligence because it is a creative concept.

People lie for as many reasons as there are lies.