A rumor repeated by enough mouths is still waiting for evidence.

Repetition builds familiarity, and familiarity is easily mistaken for confirmation. Hearing something from five people feels like five sources when it is often one source arriving five times. No amount of retelling adds evidential weight; the claim is in precisely the same condition it was when the first person said it.

Before you pass something on, ask where it originally came from. Try to trace it back one step. Most things dissolve at that point, and the habit of asking makes you considerably harder to use as a link in a chain you cannot see the beginning of.