Judging a book by its cover
All too often we see a book and for various reasons we do not open the book to find out what is inside. It could be that we don't like the look of the cover. It could be that we see just the title and back away. Perhaps we have read another book by the same author and didn't like what we read. That generally has a bearing on what the next book will be like, but it just might be worthwhile.
Does that mean we have to read every book to decide whether they are worthy of our time? No. We find out what a book is about by reading what other people say, by reading the comments from those who have read that book.
Sometimes, however, we just have to pick up the book and find out for ourselves. We might find a book, that was not highly recommended, to be very enjoyable.