The two day training for priests, outlined the "scriptural basis of evil, instructed clergy on evaluating whether a person is truly possessed and reviewed the prayers and rituals that comprise an exorcism."
According to Cardinal DiNardo, archbishop of Galveston-Houston Texas, in a phone interview, with the media said, "Learning the liturgical rite is not difficult. The problem is the discernment that the exorcist needs before he would ever attempt the rite." A priest would have to discern whether mental illness was the real cause, of someone who believed they were possessed by an evil spirit or demon. That must be difficult to discern, because if a person was possessed, I would imagine that would cause mental illness, that would be enough to cause serious mental disturbance.
Evil is very prevalent in the modern world. The effects of evil are everywhere. Current events are filled with examples of how evil intentions, thoughts and actions bring chaos and destruction in our world.
I've read accounts in the lives of saints, of how they were tormented by the "evil one," and it's clear that evil tries to undermine the good works of hard-working, sincere people. I'm very aware that evil exists which is why I pray everyday, go to Mass and try to live a good life. (I also cover myself and my family with the sacred Blood of Jesus whenever I feel threatened as I know that is a powerful statement of faith.)
Since evil is active in the world, believers should be on their guard, stay close to Christ and use the Holy Name of Jesus often in prayer. As St. Paul said, we have to "put on the armor of God" and stay vigilant.