Many of us can go through life dominated by the desires of our flesh more than our spirit. We don't realize this until we are in spiritual warfare and we aren't conditioned for what is needed.
Those who are dominated by the sinful nature think about sinful things, but those who are controlled by the holy spirit think about things that please the spirit. So letting your sinful nature control your mind leads to death. But letting the spirt control your mind leads to life and peace.