Proof by assertion is a logical fallacy in which a proposition is repeatedly restated regardless of contradiction. Sometimes this may be repeated until challenges dry up, at which point it is asserted as fact due to it not being contradicted (argumentum ad nauseam). In other cases its repetition may be cited as evidence of its truth, in a variant of the appeal to authority or appeal to belief fallacies.
This logical fallacy is sometimes used as a form of rhetoric by politicians. In its extreme form, it can also be a form of brainwashing. Modern politics contains many examples of proof by assertions. This practice can be observed in the use of political slogans, and the distribution of "talking points," which are collections of short phrases that are issued to members of modern political parties for recitation to achieve maximum message repetition. The technique is also sometimes used in advertising.
The technique is described in a saying, often attributed to Lenin, as "A lie told often enough becomes the truth", although the user may not be intentionally promoting a lie and may just believe an illogical or faulty proposition.