Do you need to take the idea of ghosts very seriously? Perhaps not, because they are not something that you can ever put you hands on, especially if you are a practical person. Are ghosts relevant in one's everyday life? Possibly not, but you really don't do not know.
Ghosts are very personal things and they are tagged to the past and places of the past. Since most people think that the past does not matter all that much, then ghosts won't matter that much, perhaps.
Our past realities define the how and the where of ghosts. The why of ghosts is more complex. Ghosts do exist, and they do come in many forms. They are a mental fact and reflect how our brain works and what our brain is capable off. If I say that time and space are the same thing a la general theory of Einstein then I might be forgiven if I say that in the future we will visit earth as ghosts. If you travel fast enough the earth will age while you remain young. As a young person you may arrive back on earth to find all your friends of a few moments earlier being presently just ghosts of the past. Yes ghosts really do exist, but we don't yet know the why of the ones we have experienced. We do know that they are possible and that our mind has many ghostlike qualities. We do know that everything we do or say continues on, otherwise Einstein would be wrong and the general theory of relativity would be false. We know that is not the case and ghosts are very real!
