All men are implicated in Adam's sin, as St. Paul affirms: "By one man's disobedience many (that is, all men) were made sinners": "sin came into the world through one man and death through sin, and so death spread to all men because all men sinned." The Apostle contrasts the universality of sin and death with the universality of salvation in Christ. "Then as one man's trespass led to condemnation for all men, so one man's act of righteousness leads to acquittal and life for all men." CCC 402
Every one of us is born into this fallen, wounded state. We remain essentially good, but original sin has led to certain consequences. We have an attraction to sin (called concupiscence), and we have a darkening of our intellect and a weakening of our will. We suffer and die. (p. 118)
Baptism erases original sin. But those consequences are still in us. (p. 118)
It may seem unfair, which many of us have said at some point in our lives, but we do see the consequences in this world. Ultimately, this is "a mystery that we cannot fully understand" (CCC 404). The Catechism Companion deals with this feeling of "unfairness" in explanation:
One way of looking at this is that we are all part of the same human family. As with our own families, the decisions and choices of family members can impact everyone - either for good or bad. Similarly, the decision of our first parents to distrust God and disobey him had negative consequences for the rest of the family - for their descendants. (p. 119)