Planetary attitude: Personal experience to ignorant

Unless I’m reading it wrong, a planet can go from personal experience to ignorance. I’m having a very difficult time imagining how this could occur within the lifetimes of the current characters. Could somebody explain how this could happen?

Thanks a bunch

Deviously effective propaganda campaigns convince the populace that the truth about Vaylen is actually out-of-date and flawed, and convincing-sounding falsehoods are trumpeted as “new scientific discoveries” and modern facts.


Your culture fought a war with them, so you know their tactics. You know what they’re about. Except that they’ve returned and they’ve changed their tactics and come in a new form…

Thank you very much it makes a lot of sense now.