Characterization of this or that person as "two-faced", as a rule, forces other people to shorten their communication with him as much as possible. This is especially true for issues related to trust or decency. But what exactly is meant by duplicity?
Flexibility is good
Duplicity is a negatively colored characteristic of a person, implying excessive moral flexibility and unscrupulousness. Despite the fact that society, in principle, is loyal to the right of every person to have one or more "masks" for different occasions, two-faced people are perceived with disapproval and condemnation. What is the difference between the usual ability to please people, adjusting to them, and duplicity?
Society makes certain demands on its members regarding relationships and socialization. These requirements, in particular, include the ability to admit that one is wrong, to look at the situation from the point of view of the opponent, the art of being interested in other people. All these qualities are recommended to be developed by psychologists and communication specialists, since they are really able to facilitate the process of communication, making it more effective. However, at the same time, people are valued in society who know how to defend their position, principles and beliefs. It is paradoxical that with all the demand for conformists, the admiration of society is caused by those who are able to fight for their views. The fact is that firmness of character and unwillingness to change one's point of view to please the majority is a necessary component for the development of human society. Almost all famous scientists were nonconformists, ready to do anything to defend their beliefs.
In ancient Roman mythology, there was a gatekeeper god Janus, who, according to legend, had two faces. Over time, the expression "two-faced Janus" became synonymous with a two-faced man, although God himself was not accused of anything like that.
Lack of principles doesn't paint anyone
As for duplicity, it is the ultimate form of conformism, that is, the ability to adapt at a reflex level. There is a saying “how many people, so many opinions,” and the problem with two-faced people is that they try to support all these opinions. Such tactics are effective only as long as the two carriers of opposing opinions do not enter into a discussion in the presence of the "hyperconformist", especially if he previously expressed support for both. Regardless of whose point of view turns out to be correct in the end, his reputation will suffer, since people rarely respect those who are not able to adhere to their views in any way.
A similar quality to duplicity is hypocrisy. The essential difference is that it is common for hypocrites to motivate their selfish actions with noble goals.
Of course, to a large extent, people are forced to duplicity by society itself, which sometimes requires from its members the opposite things: the ability to socialize on the one hand, and adherence to principles on the other. This inevitably leads to the fact that weak-willed people try to please all interested parties, paying for it with their reputation. However, one should not look for forced reasons for duplicity. Some people are able to change their principles without any external influence, just "according to their mood." It is this kind of duplicity that is particularly condemned. In the end, one can understand a person who abandoned certain views under threat to health or life, but those who easily move from one opposing side to the other of their own free will tend to be despised on both sides.