This. When you're reading a reputable textbook, you're not thinking all the time "wait is this true?". You trust the author to be correct and truthful.

Imagine being handed a textbook with a warning in the first page "10% of the facts here are made up (including this one). Good luck!"

I always assume textbooks are opinionated and full of errors. I learned that to be true at a very young age. Sometimes that assumption turns out to be mostly wrong, though, and those books are rare treasures. Most schoolbooks in particular are pretty terrible.