“I read that somewhere” isn’t a source. Find out where.

What survives in your memory is the conclusion, while everything that made it worth believing falls away: who said it, when, how they knew. You are left with the feeling of being informed, which is precisely what a wrong fact feels like from inside. Passing it on hands somebody else the same stripped-down version, and they will remember it the same way.

Next time you are about to say you read something somewhere, go and find where. It usually takes a minute. If you cannot find it, say you are not sure instead of saying it with confidence.