It means we are not perfect, we automatically do what's wrong and need to be taught what is right according to Jehovah God's standards. Sin is passed on to all at birth. Psalm 51:5, "Look! I was born guilty of error, And my mother conceived me in sin." This does not mean that proper martial relations,conception,and birth are sinful, inasmuch as God provided for marriage and childbirth; nor was David referring to any specific sin of his mother. He was conceived in sin because his parents were sinful like all humans.