A self-fulfilling prophecy is a prediction that comes true at least in part as a result of a person's belief or expectation that the prediction would come true. In the phenomena, people tend to act the way they have been expected to make the expectations come true. Self-fulfilling prophecies are an example of the more general phenomenon of positive feedback loops. A self-fulfilling prophecy can have either negative or positive outcomes. Merely applying a label to someone or something can affect the perception of the person/thing and create a self-fulfilling prophecy. Interpersonal communication plays a significant role in establishing these phenomena as well as impacting the labeling process.
Oedipus in the arms of Phorbas
Romulus and Remus nursed by a she-wolf
Krishna playing his flute with Radha
Positive feedback is a process that occurs in a feedback loop which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system in which the results of a change act to reduce or counteract it has negative feedback. Both concepts play an important role in science and engineering, including biology, chemistry, and cybernetics.
In sociology a network effect can quickly create the positive feedback of a bank run. The above photo is of the UK Northern Rock 2007 bank run.
A vintage style regenerative radio receiver. Due to the controlled use of positive feedback, sufficient amplification can be derived from a single vacuum tube or valve (centre).
A phonograph turntable is prone to acoustic feedback.
Video feedback.