In 'Insidious: The Red Door', the idea of a hidden, otherworldly realm might be inspired by true stories. There are tales in different cultures about places that are not part of our normal world, and the movie creates its own version of such a place. Also, the way the characters are haunted by a past event or entity is similar to real - life stories of people being haunted by something from their past, whether it's a memory or an actual spirit. It takes these real - life concepts and twists them into a horror story.
One true - story - like element is the concept of astral projection. In real - life, there are people who claim to have had out - of - body experiences, and this is reflected in the movie where characters enter a different realm. Another element could be the feeling of a malevolent presence. There are many real - life accounts of people feeling an unexplained sense of dread or the presence of something evil, and the movie uses this idea to build its horror.