What is the difference between acting and real life?

I was thinking that a person has a different behaviour in real life compared to a movie character. The dialogue has a different content and many little things such as being comfortable around your friends or family. In movies, the actor is a bit stiff and everything looks a bit too scripted. Should actors be a bit stiff or should they be more natural, more like in real life?
Maybe we should do a small exercise:

Hide a camera in a room and watch the dialogue that two friends have when they do not know they are being watched.

Then, try to see how that same dialogue would look like with actors.
The difference is the camera and the public. In real life, you have a connection with the person you are having that dialogue. In the movie, you don't have a connection with the person who is watching your dialogue. The public doesn't know you but somehow, the public needs to be invested in that story. It's hard to get the public to listen and pay attention

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