An author can rationally believe every line of their book, and that the book is wrong
In a book's preface, an honest, careful author often writes something like: 'Given how many claims this book makes, at least one of them surely contains an error.' Yet that same author believes each individual claim inside the book is true, having checked every one carefully. Can both of those beliefs be rational to hold at the same time?
Reveal the answer
Philosopher David Makinson argued in 1965 that yes, both can be perfectly rational, even though together they amount to believing a contradiction — that every claim is true, and that not every claim is true. The preface paradox, a close cousin of the lottery paradox, shows that rational belief doesn't automatically carry over to the conjunction of everything you believe.
— David C. Makinson, The Paradox of the Preface — Analysis, vol. 25, 1965