Oddly Wired
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sleeper effect

You eventually forget where you heard the information.

In a 1951 study, participants who dismissed a message due to an untrustworthy source began to agree with the message weeks later.

The sleeper effect occurs because the mind decouples the message from its source over time. While the source loses credibility, the content of the message persists in your memory. Eventually, the initial context is lost and the message is processed as a standalone fact.

Be careful with what you read, as you will eventually forget that you should not trust it.

Where this comes from

Study
Hovland and Weiss (1951), Public Opinion Quarterly
What the check found
The 1951 study is the foundational source for this concept, though the effect itself is widely considered controversial and context-dependent in modern psychological literature.
Confidence
Solid, with limits

Related

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