Excerpt: William Goldman's Adventures in the Screen Trade.

p.185

Why?

Obviously, I can't be -sure of the answer. The audience certainly knew a lot more about him than the way the movie originally opened.

They knew he lived alone-, in a pit of an office

They knew went to sleep with the tv for company. They knew he didn't sleep well, not when he's up before the alarm. They knew there was a woman, because of the photograph, they knew he felt something for her from the way he saluted her, they knew she wasn't with him, he was very much alone. And they knew a lot more, too - yes, he was a detective, not a successful one, and he carried a gun, so he didn't seem like someone to take lightly. The battered car told a lot about him.

But mainly it was that business with the coffee.

Whenever anyone talked about Harper to me in the weeks that followed, that was the moment they remembered -- drinking that horrible stuff. (just like the jump off the cliff is what people always mention first in Butch.) And the laugh that went along with it, that was a laugh of affection.

In a detective story of this type Maltese Falcon, The Big Sleep--all you really have going for you is your main man: You see everything, the whole world, through his eyes he keeps you company every step of the way. And if you don't like being with Sam Spade or Phillip Marlowe, not all the plot skill in the world is going to make it a happy journey. If you are turned off by your host, forget it, it's over. And if the coffee moment really turned out to be was an invitation that the audience gladly accepted: They liked Lew Harper.

From that moment forward, the script was on rails.