The answer is both! Satan is constantly working to bring chaos and death to the human race, but we also are responsible for turning against God and bringing untold sorrow into the world.
Although he is unseen and often unnoticed, Satan is constantly at work behind the scenes to disrupt God's plans for the world. Don't think of him as a cute but harmless cartoon character, dressed up in a red suit and brandishing a pitchfork. Satan is a powerful evil spirit, who works throughout the universe trying to block everything God is doing. The Bible says, "Your enemy the devil prowls around like a roaring lion looking for someone to devour" (1 Peter 5:8).
But the Bible also stresses that while Satan may influence and tempt us, ultimately we are responsible for the evil we do. Every sin we commit is an act of rebellion against God -- and we alone are responsible for it. Furthermore, sin has taken root in our souls, and it constantly bears its bitter fruit in our lives. In thought, word and deed, sin brings nothing but evil into our lives.
The most important thing I can tell you, however, is this: Satan is a defeated foe—and so is the sin that resides in us! Yes, they are still active, but by His death and resurrection Christ conquered them, bringing us forgiveness and new life. Don't be a slave to Satan or sin any longer, but by faith commit your life to Christ and allow His Spirit to control you. Christ gives us hope—hope today, and hope for eternity.