A reliable way to make people believe in falsehoods is frequent repetition,
because familiarity is not easily distinguished from truth. […] People who
were repeatedly exposed to the phrase “the body temperature of a chicken”
were more likely to accept as true the statement that “the body temperature
of a chicken is 144°” (or any other arbitrary number). The familiarity of one
phrase in the statement sufficed to make the whole statement feel familiar,
and therefore true. If you cannot remember the source of a statement, and
have no way to relate it to other things you know, you have no option but to
go with the sense of cognitive ease.

Daniel Kahneman. Thinking, Fast and Slow