The assumption the narrators influence is based on is "People who enjoy themselves after a death are unfair to everyone around them".
An inference is an act or process of inferring by deduction or induction. That is, a truth or proposition drawn from another which is admitted or supposed to be true.
The narrator is trying to tell the character not to play music on high volumes, or play scrabbles because they were not in good mood to enjoy those things. This is as a result of losing a loved one.
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