How true does a book have to be to be considered non-fiction?

I think that depending on the book, it is okay to bend the truth a little bit if it is more exciting, as long as it doesn't change the outcome of the story. I think that it isn't okay to make up large plot twists but it is okay to leave things out or not tell the complete story if you are writing a memoir to make it more valuable and exciting for the reader. However, this does not go for all non-fiction, I think that this will only work if the author is making a story out of the events. It wouldn't work in a book like Freakonomics because if the author twisted the data then the book would all be faulty information and nothing would make sense. If the book is just stating facts and is informational, a little lie can change everything so that is okay. But a memoir like the book A Million Little Pieces it is okay to exaggerate and dramatize the story to make it more interesting. There is a fine line between exaggerating and lying, and exaggerating is okay, lying is not.
On the other hand, I do think that we need a label on fiction and non-fiction so that authors do not propose ideas to the reader of what is realistic and unreal. We can learn from both type of books in different ways, but we shouldn't mix the two up. For example, when reading a true story, the reader can look at the mistakes from the past and try not to do them, or look at the lessons that the author learned. But in a fiction piece, the results are not always realistic and the reader should know that. Also, the reader should know what they are getting themselves into. Some people aren't looking for true stories, and some are, but the reader should have an idea of what is going on.