The rejection by the first humans of God's offer of friendship effected the whole of humanity. This divine invitation of a God-like condition for every human being was exchanged for mortal life and the consequential knowledge of sin. In an attempt to attain Godly knowledge of Good and Evil humankind, desiring to control its own destiny, became an enemy of God.
As sons and daughters of the first man and woman, we are born flawed. Our mortal nature predetermines our inability to fully redeem ourselves. This is expressed in the words of St. Paul: "The thing I would, that I do not; and that I would not, that I do".
"Original sin" is the hereditary but impersonal fault of Adam's descendants, who have sinned in him (Rom. v. 12). It is the loss of grace, and therefore of eternal life, together with a propensity to evil, which everybody must, with the assistance of grace, penance, resistance and moral effort, repress and conquer. (Papal Encyclical, Mit Brennender Sorge, 14 March 1937).
If Original Sin is truly a factor in our lives, so still is the presence of God. For those who accept the ravage of Original Sin as an excuse for lack of striving, is the guarantee not to accomplish otherwise attainable feats of human glory and integrity.