Back in 1950, a chap by the name of Raymond Chandler wrote an essay called The Simple Art of Murder. I'll quote the closing words:
Down these mean streets a man must go who is not himself mean, who is neither tarnished nor afraid. The detective in this kind of story must be such a man.
He must be a complete man and a common man and yet an unusual man. He must be, to use a rather weathered phrase, a man of honor, by instinct, by inevitability, without thought of it, and certainly without saying it. He must be the best man in his world and a good enough man for any world.
I do not care much about his private life; he is neither a eunuch nor a satyr; I think he might seduce a duchess and I am quite sure he would not spoil a virgin [tough luck for Nico on that one]; if he is a man of honor in one thing, he is that in all things.
He is a relatively poor man, or he would not be a detective at all. He is a common man or he could not go among common people. He has a sense of character, or he would not know his job. He will take no man’s money dishonestly and no man’s insolence without a due and dispassionate revenge. He is a lonely man and his pride is that you will treat him as a proud man or be very sorry you ever saw him.
He talks as the man of his age talks, that is, with rude wit, a lively sense of the grotesque, a disgust for sham, and a contempt for pettiness. The story is his adventure in search of a hidden truth, and it would be no adventure if it did not happen to a man fit for adventure. He has a range of awareness that startles you, but it belongs to him by right, because it belongs to the world he lives in.
If there were enough like him, I think the world would be a very safe place to live in, and yet not too dull to be worth living in.