The devil or Satan remains within the popular imagination a strange figure. Even physically, we think of a red being with horns, a tail, a chiselled chin and a mischievous smile. This figure also acts in the same way the Greek gods must have for the ancient Greeks. The Devil, as a quasi-mythological entity, tells us much about ourselves. As any psychologist will tell you, human beings often project aspects of themselves onto others. When someone says, "You are like this...," they are often discribng an aspect of themselves that they think they may share with you.
Human beings are not straight forward. No matter how open and honest you may try to be, there is always confusion, jealousy, love and hatred to stumble across and mess things up. We are not perfect. And when we identify such imperfections within ourselves this can spawn great loneliness. Feelings of unworthliness can isolate and then there is a real danger of decent.
If the devil existed he would not be a straight talker. He would says things like, "Look at so and so, she is standing happily by her husband's side while all this time she is banging his best friend." What a disastrous and devasting thing to say!
First, it makes complicated things simple. When things seem simple, action is more likely. There is no longer room for understanding or even empathy.
Second, it creates doubt. Can I really trust myself and my own judgement when someone can be so completely fooled?
Third, when we start listening to this satanic figure, what develops is dependency. A conspiracy can therefore be cultivated, fuelled by the passions of hatred so that the hypocracy of supposed 'moral' persons is pointed out and dissected.
Finally, a permissive attitude can become the norm. "These people may say that it is wrong for me to behave in such a way but they don't behave that way themselves..."
In English, the word 'confidence' tends to have two separate meanings. The first is associated with high esteem. The second, is about a trusting attitude towards a close friend or associate. In the case of the devil as I've outlined- both go hand in hand. The only way to overcome such decent (as far as I can tell) is to have confidence in oneself and to be one's own council.