If you share it before you check it, you’re part of how the rumor works.

A rumor needs carriers, and the ones who move it are mostly not inventing anything, they are passing on something that sounded likely. That is the mechanism, one unchecked forward each. Being a link is easy not to count, because you did not start it. The person it is about does not experience the difference.

Before you pass something on, ask two questions: do I know this, and would I say it with the person standing here. If the answer to either is no, hold it. Sending nothing takes no effort, and in the first hour it is the most useful thing available.