People are emotional creatures. They feel a thing, and then pick evidence that supports it and discard evidence that doesn’t.

We all do this to some extent- like when people root for a local sports team that’s kind of bad, or when someone likes a movie that’s unpopular. They’ll ignore stuff like a 10 game losing streak or a large plot hole, and focus on the one time they hit a grand slam, or that one quotable scene.

It’s mostly harmless when we’re talking about small stuff, but when it’s about history or social policy it’s a problem.