The things of the world creep in, or we have been surrounded by those things since birth. We get complacent, used to whatever it is. Just because we don't recognize the negative changes in ourselves, usually it's a little at a time, doesn't mean it's not there. Like when your hair grows longer. You don't see it growing, day by day, until it's bushy and needs trimming. Yet other people see it. Another example, violent games/movies/music. Our hearts get hardened to it, the more we do it, and we don't see the effect it's having on us, until God shocks us back to His reality, or when we stop doing it for a while, and then see it again, it's not so appealing anymore. The Lord's Spirit will stir within us, and show us that it's unpleasant, or a sin.
As we change, through the Holy Spirit guiding us through life, and our hearts soften, we become more sensitive to those things, and they become offensive to us. As he purifys us with His wisdom, and we become more holy, we will turn away from the things of the world that are violent, oppressive, or distracting from God.
Sometimes it's a gradual education from the Lord, and sometimes it's a powerful awakening.