What constitutes infallibility of Quran?

Muslims regard the Quran as infallible and containing in itself evidence of its own veracity (correct me if wrong). I have read many claims that attribute that status to a lack of contradictions of accounts that are conveyed within the book. However, I do not understand why an absence of contradictions within a book should designate it as divine. I find that it would be rather easy for a human to write a book of such closely crafted content whereby no two ideas or positions presented would be conflicting one another. In that case, what is it exactly that constitutes the revered infallibility of the Quran?