The body has the way. The mind loses the way.
I see being undead as a cruelty. Even a thievery of your right to rest in peace. I guess it would be a curse if you really wanted to be mean to someone. Well, regarding curse related undead, as it is a common branch, the process goes like this.
You become passionately, even perhaps violently, entangled in another person’s life. You are either the victim of their actions, or for one reason or another the focus of their attention. The intense energy shared between you and this other person creates a sort of karmic chain or curse, and while the issue remains unresolved, they are unable to rest or move on emotionally. This is a rare case, but there are stories of it.
Now in no case is the undead involved under any compulsion to see the light necessarily, admit the wrong doing, or offer any forgiveness. So this state can persist perhaps even beyond the point at which the life situation has ceased to exist.
Because it’s not a real soul? In this case, it would be the real soul. People can become transcendently angry, or experience all-consuming despair, and remove the limitations or safeguards of the flesh. These forces can reach incredible states of empowerment to the point that they not only haunt an area, but exert an impact on an entire community, distorting the feel of an entire town or even city, for example, and affecting the minds of all who live there to one degree or another. Some of the places in southern Louisiana. Some of the islands off the Italian peninsula. Haiti as a whole. Jamaica to some degree as well.
Did they make a pact with the devil, like someone said? No. That is more often than not a blind sociological/cultural prejudice, but pacts with the devil occur all the time in a way. Whenever a consensus is set up that is primarily defined by a leader, or group of leaders, who have devilish characteristics.
How is a banshee formed? Oh, a banshee, perhaps more generically called a wailer. A wailer arises when someone with an intense fear of loss and death dies themselves. They lose a sense of the difference between life and death and become very confused to the point of often mistaking what faded impressions they get of the living as an encounter with the dead.
They think we are dead and they scream at us. Yes, out of panic driven fear. Now given time, a wailer becomes a bit acclimated, withdraws into a sort of morbid dream state.
This must be what it’s like to be a ghost, people always screaming at you. I could see where someone would get so tired of that they might decide to embrace it and have fun. Well, when they get too relaxed they actually move on, because it’s a strain not to, like a total body migraine. But with the long-time wailer, they begin to notice that there is a difference in the shades they see. This is why banshees are connected to being able to predict death. When one shade becomes more vivid to their vision, they panic yet again. The person often slips over the veil not long after that.
Your thoughts are welcome. Be well friends.