Why do not we always remember our dreams?

It is possible to control the content of his dreams. This is called lucid dreaming: dreaming with a sense of being in a dream. These lucid dreams have long been the subject of controversy, but their existence has been conclusively proven in the 70s. They are defined as a "mixed state, an overlap between REM sleep and activated processes corresponding to the awakening."

These dreams are different degrees and only 10 to 20% of the population regularly. These are most often women and young people. Lucid dreams are to the simplest interrupt a nightmare by saying that "just a dream" and wake up a few seconds later.
But some people go much further in control of their dreams. They are able to modify the content of their dreams, for example, their practices. It is also used for patients who suffer from repeated nightmares. For this control, simply to be "motivated and possess good skills spontaneously dream recall."