Oddly Wired
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truth

You repeat a false statement until you believe it.

The illusory truth effect describes the tendency to believe repeated information is more credible, a phenomenon first established by Hasher, Goldstein, and Toppino in 1977.

While the 1977 study established the effect, the finding that it persists even when subjects have prior knowledge to the contrary was identified in later research, such as Fazio et al. (2015).

The more you hear a lie, the more your brain treats it as fact.

Where this comes from

Study
Hasher, Goldstein, and Toppino, 1977, Journal of Verbal Learning and Verbal Behavior
What the check found
The core effect is well-documented, but the claim incorrectly attributes the 'even when you know better' finding to the original 1977 study rather than subsequent replications and extensions.
Confidence
Solid, with limits
truthcognitionrepetition

Related

One of these every day, and every one names the study it came from. When a finding is contested, it says so.