can we distinguish between the criminal and the crime?

A major human question is one of “nature” vs. “nurture” - does a person’s environment determine their behavior, or is their behavior determined by their innate character. At the end of Chapter 17, Poirot’s allegorical story about a weak man who, when desperate enough or provoked in just the right way, is moved to commit a crime, articulates the novel’s stance on this debate. It is the precise combination of a weak character and the right circumstances (both nature and nurture) that create a criminal. In the case of Dr. Sheppard, it was his “streak of weakness” combined with the opportunity to make easy money, and then the desperate need to hide his behavior, that provoked him to commit murder. Sheppard is not a sociopath or a hardened criminal, merely a weak man who was put in a tempting, and then challenging, situation. There are other characters in the novel who embody this theme. Flora declares herself a weak character, and it is this weakness combined with a desperation for money that caused her to steal from her uncle. Ralph, also described as weak, was moved to break his marriage vows and become engaged to his step-cousin when he recognized the opportunity to get out of the crippling debt he found himself in.