Not only does Satan's deception play a part in man's separation from God, but God's Word also shows that there is a willfulness involved in man's choice of the direction in which he is headed. Men "suppress the truth in unrighteousness, because what may be known of God is manifest to them"!
In his deception, Satan has been so forceful, his argument so "good," that sincere men will argue and fight against God, thinking they are serving God. Jesus prophesied that people will kill in the name of God and think, sincerely, that they are doing God a service (John 16:2). How effective Satan has been—and is—with his deceptions!
If he has been that effective in deceiving people, how wide is the gulf that separates mankind from God? It is so wide that in the Parable of Lazarus and the Rich Man in Luke 16, it is described as "impassable," and so it is. Sin brought death, and for humans to bridge the gap to eternal life is impossible.
Mankind is in a horrible state when one looks at it from the evidence that God has on His side. We deserve every bit of pain, torment, hurt, and anxiety that might come our way. We have no basis at all for complaining to God that we deserve His mercy and forgiveness. God has every right, based on our sinful activities, to do what He could do, but in His mercy, will not do.