How we change what others think, feel, believe and do
The need for: Conformity
Have you ever suddenly noticed when you were in a group of people where they all were doing or saying something different to you? Did you feel uncomfortable about this? Did you feel an unspoken pressure to go along with the rest of the group? If so, you were simply complying with your need to conform.
The need for conformity is the desire to go along with the norms of a group of people, so you will be accepted as an in-group person (and not rejected as an out-group undesirable person).
We are a tribal animal, which leads us to have a deep need to belong to a group of some sort. Conforming to group norms is a signal to the other group members that 'I am like you. I am following our rules. I am not a threat.' This signal indicates your consistency of behavior, allowing the other people to predict what you will do. It is also a step along the way to increasing your esteem within the group.
Different groups have different norms or rules to which group members conform. This can be to do with behavior, attitude, dress, language, etc. The degree to which other people conform to the rules indicates their desire to be a group member.
In-group members who conform strongly are core group members who are asserting the identity of the group, or peripheral members who are trying to impress the core members, perhaps to be accepted into the 'inner circle' (which is in fact another group-within-the-group). Further out, people outside the group may similarly emulate group members either to seek admission to the group or to form an admiring group who are seeking to gain some reflected glory. An example is pop fans who dress like their idols.
Conformists and non-conformists
The strength of desire to conform is a personality trait whereby some people will try to conform to whatever group they are in at the time, whilst other 'non-conformists' will go in the other direction, deliberately asserting their individuality by rejecting all but a very few sets of norms. Teenagers come to mind, as they reject their parents, being non-conformists in the family, whilst desperately conforming with peer-group norms as they seek acceptance by the cliques and gangs of the schoolyard.
Some groups are mutually exclusive, where the rules of one group are that you are not a member of specific other groups. Gangs and families are an example, as are political parties and different religions.
If you want to persuade someone, it helps a great deal to gain their trust by being in the same group as them. An approach that can help this is to conform with their group rules.
Strict conformity to others' rules can be seen as an invasion or ridiculing. For example a senior manager going down to a factory floor may well be viewed with anger if he changed into a set of overalls and plastered grease on his face. In such cases, going some way toward the other's norms can be effective. For example the senior manager may remove his jacket and tie and roll up his shirt sleeves.
You can also be in the reverse situation, where you set the rules and the other person has to conform to your rules in order to gain admission to your group and the other benefits that this will confer. Once within the group, the threat of expulsion will then keep them conforming. Cults, religions, companies and many other groups use this to coerce people into all sorts of peculiar behaviors.