We see just how quickly the results of the first act of rebellion show up and how others are drawn in. Notice, too, how in Cain's experience, one sin led to another. But his anger and resentment show that he was more concerned about his own reputation and pride than about pleasing God. Abel had the right attitude - there was humility and reverence. That is what pleases God.
Sin has to be resisted.
Once we let a wrong idea in, it will slowly take over until it controls us. Recognise the power of sin - 'crouching' like an animal waiting to spring. Be ready to fight it with God's help. Our newspapers often contain stories of people just like this. Other people get in the way so they are disposed of by murder, divorce, dismissal or just by being ignored.