People often mistake familiarity with an idea for evidence supporting it.

An idea heard often enough begins to feel established. The mind registers ease of recall and treats it as evidence, so repetition produces a sense of confirmation without a single additional fact having been supplied. This is why slogans work, and why things you have simply been around for years feel more certain than things you learned last week.

When something feels obviously true, ask whether you can name any actual support for it or just remember hearing it. If it is only the second, treat it as unexamined rather than settled. Familiarity is a fact about your exposure, not about the claim.