A prominent theory involves the reduction of restraints, put forth by Fritz Redl in 1949 and analyzed in depth by Ladd Wheeler in 1966.
[5] In 1980, Freedman et al. have focused on the effects of physical factors on contagion, in particular, density and number.
Multiple sources, especially close friends, can make imitation legitimate, credible and worthwhile due to collective effort put in.
Even though close friends can strongly influence each other, they will not help each other learn about new opportunities, ideas or behaviours in socially distant settings if they all know the same things.
Few 'weak' and 'long' ties can help spread information quickly between two socially distant strong networks of people.
On the other hand, complex social contagion processes require multiple sources of influence.
This is not possible with few 'weak' ties: they need to be long and multiple in number to increase the probability of imitation between socially distant networks.
Once the restraints are broken or reduced the observer is then "free" to perform the behavior; this is achieved by the "intervention" of the model.
... [The] initiator, by his action, establishes an inequitable advantage over the other members of the gathering which they may proceed to nullify by following his example.
[5] Freedman (1975) put forth the intensification theory, which posits that high density makes the other people in a group more salient features of the environment, this magnifying the individual's reaction to them.
For instance, a person might praise and go to a restaurant with good food based on others’ recommendations but avoid it when it becomes over-crowded.
The more followers someone has, the more overloaded they are with information and lower the chances that they will retweet a particular message due to limited attention.
[2] Rather, social contagion can amplify amongst 'ordinary' users with low following if they are closely connected in a peer network.
Hence, social contagion can occur efficiently amongst tight community structures, in the absence of prestigious and dominant leaders.
[6] Gino, Ayal and Ariely (2009) state that an important factor influencing contagion is the degree to which the observer identifies with the others of the group (p. 394).
[18] However, high homophily or the likelihood of being connected to others with similar interests, can lead to both minority and majority groups overestimating their sizes and vice versa.
This can cause people to falsely predict the frequency of their behaviour in the real world since they estimate based on their personal networks.
[1] In the original Milgram experiment on obedience, for example, where participants, who were in a room with only the experimenter, were ordered to administer increasingly more severe electrical shocks as punishment to a person in another room (from here on referred to as the "victim"), the conflict or social restraint experienced by the participants was the obligation to not disobey the experimenter – even when shocking the victim to the highest shock level given, a behavior which the participants saw as opposing their personal and social ideals (Milgram, 1965, p. 129).
In the first of the two experiments, "Groups for Disobedience", the confederates defied the experimenter and refused to punish the victim (p. 130).
The group success in one case and failure in another can be traced directly to the configuration of motive and social forces operative in the starting situation."
This effect could not be explained by self-selection (homophily) or shared built environments and is attributed to social contagion.