Detachment is being disconnected from one's self, like being an outsider, having the quality of being objective, impartial and unbiased, which therefore will mostly result in fairness and having a precise state of mind to undertake certain task.
That state of mind helps novelists to use their techniques of language and composition in a very efficient way, allowing the critical process to be accurate and for the novelists keepsake of being writers, holding the balance and avoid prejudice or passing judgement on their characters.