When a sentence starts with “everyone knows,” that’s exactly the time to check.

That phrase does not supply evidence, it stands in for it. What follows is usually something that spread widely enough to feel settled without anybody recently confirming it, so the confidence comes from repetition. Common knowledge is often just old knowledge. The consensus that makes it sound safe is exactly what stopped anyone checking.

Next time you hear it, or catch yourself saying it, take two minutes and look. You will be right most of the time, and the exceptions are worth finding. Doing this occasionally is enough to keep you from repeating a few things you would rather not have.