Now look at Mary Astor. She was thirty-five when she made this picture. Does she look like a damsel-in-distress? Hell no.
Imagine a different actress playing Brigid. Say Gene Tierney. At twenty-one Gene could have totally sold her helplessness. And then when Sam Spade says, "You're very good. It's chiefly your eyes, I think, and that throb you get in your voice...," think how we'd feel. What is wrong with Spade—does he hate all women? In the end, we'd realize that our detective knows a whole lot more about human nature than we do.
Who would you choose?