How Sin Works Itself Out

Sin began long ago. We were all there in Adam. Adam acted on our behalf and plunged our entire race into a plight worse than death, we became sinners. As sinners, we do exactly that, sin. Sin is not just a heart problem, although it primarily is a heart problem. It is also an action problem. We do exactly what we want to do. We sin. We do not sin to become sinners, but are sinners who simply act. Those acts are sin.
Again we look to James for a little insight into this phenomenon.

Then desire when it has conceived gives birth to sin, and sin when it is fully grown brings forth death. (Jam 1:15)

That is how sin comes out. After our sin nature begins to lust and crave after sinful things, we sinners act on those lustings and cravings. That is how sin works itself out in our lives.
We long for intimacy, and then our depraved natures take over to find how to find intimacy. Intimacy though is transformed by our sinful imaginations into a lust for something that is not the pure intimacy of love for our spouses, but an adulterous affair, an x-rated movie, or a pornographic magazine. Something that purports to be intimate, but is really detached enough so that we do not have to invest any time or effort into the intimacy.
We long for a loving relationship with our children, but our depraved natures twist this into child abuse, anger and even hatred for our children.
We long for a relationship with God, but again our natures step into the way and turn this into idolatry, false worship, and self-love.
We are a twisted, depraved race. And we have only one hope. We need a new nature. But the new nature will not help us because we have incurred the wrath of Almighty God on ourselves for our sinfulness.
Going back to the beginning, we were created for God. God made us for Himself, a human race to glorify Him. But we have not fulfilled that purpose. Instead we have become creatures that openly defy and rebel against their Creator. We are guilty of treason against the One who alone rules the world. We have lifted up ourselves over our God and attempt to rule ourselves without His sanction. We are a world of six billion little puny kingdoms setting themselves up against each other and ultimately against God.
But judgment will come.