People aren't books.

Books are static. Unless there are appendices and supplemental volumes of world-building and backstory, all the information a reader gets is what's on those pages. Any omission the author makes tends to be by design, and the story stays the same no matter how often the reader cracks that book open. (Barring later editions and whatever happens when e-book platforms decide to change things around.)

Reading a book isn't the same as reading a person. Experience might not be enough to tell what was behind that look, or which moves stick and why, and it certainly won't be able to tell just how much alcohol was involved in the exchange of sob stories. (Like it or not, looks like that old equine adage is still kicking.)

It isn't just emotion that causes problems. Incomplete information has its part in belly flops too.