I'm beginning to think that most noir plots, like most horror plots, depend on the protagonist not recognizing what genre they're in. It's a little easier to sympathize with the horror protagonists -- it's not terribly unreasonable to suppose that your child's invisible friend is imaginary, or that the noises in the basement are mice, or that precautions that would be sufficient against most criminals will have any effect whatsoever on Michael Myers; whereas most noir plans would go astray even in real life, never mind in the universe of Double Indemnity.