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A set might be {1, 2, 3} and a list might be [1, 2, 2, 1, 3, 2, 3, 1, 2, 3] (which when converted to a set is identical to {1, 2, 3}. But a Map is {"Campbell" ↦ "beginning", "Rob" ↦ "General", "Janeice" ↦ "beginning", "Maneesh" ↦ "Swing"}.
A Map keeps all its data in a different form: pairs, forming a function. So it has to handle those data differently.