I think everyone realizes that sin is bad, and we all know passages such as "The wages of sin is death" (Romans 6:23). But I wonder if people really and truly understand how far-reaching the consequences of sin can be. In my own extended family I've had the unfortunate "pleasure" of seeing this for real.
In my wife's family there is a married couple who have four young children. Over the last couple of years the wife has had multiple affairs and has lied to cover her indiscretions. Yes, this is bad, and an obvious breaking of God's commandment against adultery. Even simply the lies are against God's Word. She has been very selfish in her actions, and though her husband hasn't always been the best of people and the most attentive spouse or father, he hasn't gone to the extent that she has. But let's look at the spiral this has caused.
Her children are being pulled between the parents and are being affected by those stresses.
Her mother and father have had their jobs affected by the stress of dealing with her.
Her hidden sin has affected the church around her.
Her Christian witness has been ruined and she cannot effectively serve in church.
Her family doesn't trust her at all.
Her sister doesn't want to be around her.
And that's just the beginning. At a quick count I can think of at least 13 people in her immediate family alone that have been directly impacted by her poor choices and sinful actions.
God has set up "rules" and guidelines, defining certain actions as sinful. This isn't because He wants to be a dictator and run our lives. It's because He knows that these actions have far-reaching consequences and can destroy not only us but those we know and the lives we touch.
Before you act selfishly and act against God, really think hard about who you are really affecting. It's more than just yourself.