Fast forward a dozen episodes and perhaps the most important step in the character arc of Walter White is taken when he deliberately refuses to save Jesse's girlfriend Jane from asphyxiation on her own vomit. Put simply, Walter stands and watches as Jane dies. This is critical. It was the second character of the series dead at Walt's discretion but the first who'd done nothing to threaten him. Jane wasn't innocent, nor a particularly great person, but she was helpless, harmless and, ultimately, expendable in the eyes of Walter. In this moment, he chose his work over his respect for human life... and a lot of bloodshed followed as a result.