How Do We Even Know that We Lack True Happiness?

They have known it then, I know not how, and so have it by some sort of knowledge, what, I know not, and am perplexed whether it be in the memory, which if it be, then we have been happy once; whether all severally, or in that man who first sinned, in whom also we all died, and from whom we are all born with misery, I now enquire not; but only, whether the happy life be in the memory? For neither should we love it, did we not know it. We hear the name, and we all confess that we desire the thing; for we are not delighted with the mere sound. For when a Greek hears it in Latin, he is not delighted, not knowing what is spoken; but we Latins are delighted, as would he too, if he heard it in Greek; because the thing itself is neither Greek nor Latin, which Greeks and Latins, and men of all other tongues, long for so earnestly. Known therefore it is to all, for they with one voice be asked, “would they be happy?” they would answer without doubt, “they would.” And this could not be, unless the thing itself whereof it is the name were retained in their memory.

Augustine, Confessions, Book 10.29

How do we all have some sort of inner knowledge of the happy life, enough to know that we do not have it and are always secretly longing for it? Perhaps, Augustine says, we have all inherited the memory of true happiness, the memory of Eden, from Adam. I have read that research shows the effects of trauma can be passed on to generations of those who have not themselves experienced that trauma. What a powerful thing then, Eden, and its loss, must have been such that seven billion humans, when they are honest with themselves, still feel it in their bones.