According to the Bible, it tells us that the imaginations of man's heart is evil continually. There was even a time where God said He regretted creating man because of their evil ways. Most of the things we face in our world today as results of the actions of people. When the devil rebelled against God He sent the devil and his cohorts down to earth.
The devil now takes the position of as the god of this world. He poisons the heart of men and lead them into commiting evil in the sight of the Lord. Some of the things that we see people do wasn't done on their own accord, some are being controlled by the devil.
When we become born of God we become new creatures. The adam-ic nature we were originally born of seizes to exist. We become cleansed and purified inside out through the blood of Jesus Christ. We become transformed through the spirit of God and His Word when we continuously study it. We can only experience this transformation when we allow ourselves to be ruled completely by the Holy Spirit and not by man or by our flesh.
Only when we live in absolute obedience to the Word of God and walk in His ordinances do we make it impossible for the enemy to have control over us.