Johnny Mac wrote: “That’s a good question. Did Stick misread the signs? Were there any signs? Did Arlene even know what she was going to do.”
Stick blew it because he told his business to a woman. Period. Forget the rest. You get into ‘I think I can trust her’ and it’s the beginning of the end. At least that would be the clear answer per Frank’s 10 Rules of Robbery, or whatever he called them.
The guiding principle of Frank’s Rules would be ‘don’t tell anyone and no one can rat you out.’
And it’s not just women. I think every person in the book who knew what Frank & Stick were into tried to or succeeded in screwing them over. Sportree, Leon Woody (one of my all-time favorite character names, btw), as well as the little black girl who worked at Hudson’s (Marlys?), and Arlene.
Clement Mansell, the Oklahoma Wildman, knew that good present intentions can change with circumstances, like arrest and the threat of prison. He told Sandy Stanton that. So even if Stick was positive Arlene meant what she said when she said it, he should have known he was on a slippery slope.
Bottom line: why go through all those changes? Just keep your mouth shut and ease your mind.