They will seek to justify this sadness in their personal lives. By concentrating on sad music, the sadness tends to materialize itself in the listener's personal life. Emotion is one of the great tools we use in creating events. Sad emotions tend to instigate physical events pervaded with sadness. You may even unknowingly move into a more dangerous neighborhood or part of town as this belief objectifies itself.
Beliefs can create nightmares.
A belief that you aren't a worthy person, regardless of where it comes from, will create nightmare-like qualities in your waking and dream lives. You will find facts to support it. You will seek out people who believe in it. This will assist you in forming a pleasant future and avoiding many nightmares both while you are awake and while you are asleep.