@candyquilt-- Verisimilitude doesn't actually have anything to do with literature being fiction or non-fiction. It's more about believability. People can relate to and believe in fiction too. Regardless of which genre a piece of work fits into, people should be able to relate to it. They should feel that it's possible, that it could happen to them. Or they should relate to the characters, their worldviews and their actions.
Without this connection, the reader will not be drawn into the story. So when people say that a book doesn't have realism or verisimilitude, that's another way of saying that they couldn't connect with the book.