Utility is the pleasure, happiness, or satisfaction obtained from consuming a good or service. This relates to purposeful behavior because consumers act in a purposeful manner to ensure they maximize satisfaction or utility. Weighing the cost and benefit of their decision is purposeful and done so to ensure that their utility is increased to a reasonable level.
Work Step by Step
Human behavior is focused on self interest. Seeing as utility is the maximization of a human's happiness, pleasure, or satisfaction it would make sense that humans act in a purposeful manner to increase their own happiness.