The answer to these questions can be found, not surprisingly, right at mankind's genesis. Genesis 4:7 to be exact. When Cain's offering to God was rejected he became angry. God confronted him and said something very interesting. He said:
"...sin is crouching at the door. Its desire is for you, but you must rule over it." (ESV)
You must rule over it. I get the picture of at lion or tiger, hungry for a fresh kill waiting just on the other side of the door, in the dark, waiting for me to step outside and into its claws and jaws. Scriptures tell us that Satan is like a roaring lion seeking whom he might devour (1 Peter 5:8), so I suppose the picture is apropos. But I don't think we (myself include) take this admonishment by God to Cain seriously enough. We play with sin.
I'm reminded of the stories of lion and tiger trainers who, during a live performance, are mauled to death by the animals they have trained. Everything is going as planned. This show is going like every other show before it when suddenly the lion acts just like lions do: a wild animal. One minute the trainer is in control and the audience laughing and clapping. The next the trainer is on the ground dead, lying in a pool of his own blood and the crowd is no longer laughing, no longer clapping.
James once wrote along similar lines when it came to sin. He wrote:
But each person is tempted when he is lured and enticed by his own desire. Then desire when it has conceived gives birth to sin, and sin when it is fully grown brings forth death. (James 1:14-15 ESV)
The fact is sin never starts where sin ends. That is, the only way you got where you are is you started somewhere. You played with the lion and thought you were clever and in control but woke up one day to find yourself lying in a pool of your own blood, dying. Don't play with sin. Stop it now. Run away, far away. Now!