Men often oppose a thing merely because they have had no agency in planning it, or because it may have been planned by those whom they dislike.

Hamilton is pointing to a recurring motive in political and organizational life: opposition that springs less from the merits of a proposal than from wounded pride, factional rivalry, or personal animus. People may resist an otherwise sound plan because they were excluded from its design (a loss of status and influence) or because credit would accrue to opponents. The remark underscores how decision-making can be distorted by ego and party spirit, implying that wise governance requires mechanisms—and personal discipline—that separate evaluation of policies from the desire for authorship or the impulse to thwart disliked figures.