Here’s an interesting quote from William Walker Atkinson:
“One of the most striking instances of the power of the radioactivity of thought, and of the inductive action of thought, is found in that class of phenomena which has been called “thought‑contagion” or “mental epidemics.”
As these terms indicate, in this class of phenomena there is a “spreading” of thought‑influence and a liability to “catch” the spirit of the general thought‑wave which is spreading itself over a group of people, a community, a nation, or even over the civilized world as a whole.
In its simplest form, thought‑contagion is found in cases in which groups or congregations of individuals are moved by a common impulse, the latter being originally imparted by some individuals of strong emotional tendencies in the crowd, and then rapidly spreading from one to another of the crowd until nearly everyone in the group or crowd has “caught” the feeling and its accompanying impulse. This class of phenomena, in its simplest phases, is illustrated by the rapid spread of emotional excitement among an audience or congregation under the influence of a magnetic orator, preacher, actor, or other “spellbinder” as the colloquial term well expresses it.
You have seen large audiences swayed by a common emotion under such circumstances; and, perhaps, have yourself come under the influence of the epidemic thought‑currents. One is often roused to the stage of intense emotion, and experiences the impulse to act thereupon, by words which when seen in cold print seem devoid of any exciting power. In such cases,
the orator, actor, or preacher possesses sufficient magnetic force to “set things going,” and after that the contagion spreads rapidly until finally nearly every one in the audience is more or less affected. In cases of “revival meetings” the influence of thought‑contagion is quite strongly manifested.
The same principle governs what are known as “mobs,” creating what is known as “the mob spirit.” The mob, at the beginning, may be made up of the average persons of the community, brought together by curiosity or general interest, and free from vicious intention. Before long some turbulent
spirits in the crowd begin to manifest emotional excitement, and start to arouse a similar feeling in their neighbors. If the conditions are favorable, before long the contagion has spread and the epidemic has assumed alarming proportions. If the impulse and influence be sufficiently strong, the crowd veritably becomes a “mob,” and in some cases proceeds to commit acts of violence and destruction of which the majority had no thought in the beginning, and of which but few of its members would have been capable under ordinary circumstances. When the influence has passed, most of the individuals are aghast at the acts which they have helped to perpetrate.
Let us remind you that “in knowledge there is power,” in this matter of thought‑contagion and influences. A knowledge of the facts is in itself a strong weapon of defence. Again, let us assure you that there is nothing to fear in the case. That is, “there is nothing to fear but Fear”—for Fear is the great negative, depressing, weakening mental state. Fearthought invites undesirable mental‑currents and contagion; Fearlessness repels them. Fearlessness is positive; Fearthought is negative; and the positives always overcome the negatives.”