ad nauseum - repeating something over and over again, until it forms a mental association and/or becomes perceived as truth.

Based on the "mere exposure effect," which is a psychological phenomenon by which people tend to develop a preference for things merely because they're familiar to them, including things they don't like. This principle for example makes people more likely to prefer listening to a song they've heard before over a new song they've never heard and to believe something they hear repeatedly, even if they know it's untrue.

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