The dead are quite indifferent to things left behind on earth unless they are so materialistic, selfish, possessive and so attached to bodily and earthly possessions that they could not forget them even after death. When this happens, the souls becomes earth-bound and begins to haunt the living. This is one reason why they are Ghost. Earth-bound spirits are the unclean spirits. These poor souls don't even realized they are already dead, so they keep on doing the same things they were doing while alive.
Spirits who make themselves visible to console are those who are left behind. But not to frighten you, just to prove that they exist. To deliver an important message, to give advice and ask for spiritual help for themselves. Contrary to popular belief, spirits appear not only at night but even in during day time. They don't choose a particular hour or day within which to appear, except for a very special reason perhaps. Spirits, in reality can be seen only by soul.
What should we do if we encounters a spirit or an apparition?
* Ask the spirit who he/she is? wants? what way we can help? The apparition may have wanted to give an important message or need someone to pray for his/her wandering. Sometimes spirit doesn't know that his/her already in spirit world and need to be reminded of it.Source: Understanding the Psychic Power
of Man by Jimmy Licauco