As Vico stated, pride is inordinate self-esteem, self-love; ordinate self-love being a good, a gift from God. Another way it’s been described is as an inordinate desire for one’s own excellence. Adam’s desire was to be like God-a good thing in itself-but he wanted to be like God while apart from Him, autonomous from Him. This is where the injustice lay; this is where Adam sinned, because he held himself up to be equal to or superior to God. What could allow for this “defect”, the defect of the creature failing to recognize his “creaturely status” as the CCC 398 puts it?:
398 In that sin man preferred himself to God and by that very act scorned him. He chose himself over and against God, against the requirements of his creaturely status and therefore against his own good. Constituted in a state of holiness, man was destined to be fully “divinized” by God in glory. Seduced by the devil, he wanted to “be like God”, but “without God, before God, and not in accordance with God”.
IMO the main “defect” of Adam was simply that he wasn’t God. When combined with other facts, such as the fact that Adam was given the gift of reason and also of free will, the ingredients are present for a potential fall; Adam could, by virtue of being a limited, finite, creature, make a wrong choice; he could believe a falsehood about himself; he could sin. He could commit an act against his own nature even if he was adequately equipped to not make such a choice. Freedom carries with it responsibility.