What is the reason why "buy longevity" looks for "double body" in superstition?

The story of Body double is not credible. According to folklore, a ghost who died in vain will look for body double where he died, so that he can be reincarnated. This is an unreasonable statement. Taoist theory holds that people have three souls, and one soul will always be caught by ghosts after death. And those wandering ghosts are another soul of human beings, and this soul can never be reincarnated and should go to Lingfu. But these wandering souls are attached to the world, so they stay in the world. The idea of buying longevity is somewhat credible, because it is related to ghosts and gods. The so-called "don't ask heaven, ask ghosts and gods." If the gods don't help, they have to think of ghosts and seek immortality.