https://www.sciencedaily.com/releases/2019/12/191203094813.htm

In a series of experiments involving more than 2,500 people, Daniel A. Effron, a London Business School associate professor of organizational behavior, and Medha Raj, a PhD student at the University of Southern California, found that seeing a fake headline just once leads individuals to temper their disapproval of the misinformation when they see it a second, third, or fourth time.

The findings, published in Psychological Science, have important implications for policymakers and social media companies trying to curb the spread of misinformation online, Effron says.