The ability to determine that a person is not confident in himself is necessary not in order to “suppress” him, but in order to have the opportunity to test himself.
This is important if only because a manipulator from your environment can take advantage of the signs that you broadcast.
What signs are we talking about?
So, non-verbal behavior is especially eloquent in an insecure person. This is a "shifting gaze", when a person avoids looking you straight in the eye, stooping and hunched back, incoherent speech.
Uneven breathing also indicates insecurity: your interlocutor tells you something at a fast pace, after which he is forced to stop in order to take a breath.
You should also be wary if you notice nervous gestures. Often people with this character trait fidget with something in their hands or wring their fingers.
In addition, a clear sign is frequent touching - a person may touch their face or hair, constantly adjust an item of clothing or brush away non-existent dust particles.
Finally, an insecure character is given away by being distracted by the watch, phone, and other people, as well as frequently changing positions.
