The way that Mary’s careful planning influence the outcome of the story is as detailed below.
From sources online, this question is taken from the story titled "Lamb to the Slaughter" written by Roald Dahl.
In the story titled "Lamb to the Slaughter", we see that Mary is a devoted wife who nevertheless kills her husband when she finds out that he wants a divorce. When she killed him, she coldly and carefully planned a way in which she will not be accused of the crime. Thus, that influenced the outcome of the story, which ensured that Mary was not blamed for the murder.
For example, Mary went out after the murder and talked to the grocer for a while and that allowed Mary to have an alibi in case she is considered a suspect.
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