Part of the problem is that a lot of people are legitimately delusional, and the correct answer for them in their lives is, in fact, "discount your personal observations (they're not real)".

Like, if Fox news tells some people that San Fran has a ton of crime, then they will start seeing that crime. They will observe it. But that doesn't mean that crime has actually went up. It means they were primed and that they are biased.

When your political opinion relies on some set of facts being true, then you will just believe those facts to be true, ala 1984. And then to you, they are true. Your eyes can most definitely deceive you.