I'm not sure whether you mean repeating it to oneself or to someone else, but in case the latter, then:

Propaganda

From the Wikipedia article "Propaganda techniques":

This uses tireless repetition of an idea. An idea, especially a simple slogan, that is repeated enough times, may begin to be taken as the truth.

One definition of propaganda is:

Information that is spread for the purpose of promoting some cause.^Source

Repetition is essential to propaganda:

But the most brilliant propagandist technique will yield no success unless one fundamental principle is borne in mind constantly and with unflagging attention. It must confine itself to a few points and repeat them over and over. Here, as so often in this world, persistence is the first and most important requirement for success.

^{Mein Kampf, Adolf Hitler, 1925. Translated by Michael Ford, 2009. Emphasis mine.}

I'm not sure whether you mean repeating it to oneself or to someone else, but in case the latter, then:

Propaganda

From the Wikipedia article "Propaganda techniques":

This uses tireless repetition of an idea. An idea, especially a simple slogan, that is repeated enough times, may begin to be taken as the truth.

^{Emphasis mine.}

Repetition is essential to propaganda:

But the most brilliant propagandist technique will yield no success unless one fundamental principle is borne in mind constantly and with unflagging attention. It must confine itself to a few points and repeat them over and over. Here, as so often in this world, persistence is the first and most important requirement for success.

^{Mein Kampf, Adolf Hitler, 1925. Translated by Michael Ford, 2009. Emphasis mine.}

I'm not sure whether you mean repeating it to oneself or to someone else, but in case the latter, then:

Propaganda

Information that is spread for the purpose of promoting some cause.^Source

^{Mein Kampf, Adolf Hitler, 1925. Translated by Michael Ford, 2009. Emphasis mine.}

I'm not sure whether you mean repeating it to oneself or to someone else, but in case the latter, then:

Propaganda

From the Wikipedia article "Propaganda techniques":

This uses tireless repetition of an idea. An idea, especially a simple slogan, that is repeated enough times, may begin to be taken as the truth.

One definition of propaganda is:

Information that is spread for the purpose of promoting some cause.^Source

Repetition is essential to propaganda:

But the most brilliant propagandist technique will yield no success unless one fundamental principle is borne in mind constantly and with unflagging attention. It must confine itself to a few points and repeat them over and over. Here, as so often in this world, persistence is the first and most important requirement for success.

^{Mein Kampf, Adolf Hitler, 1925. Translated by Michael Ford, 2009. Emphasis mine.}