Re-doing an old idea.

I'm going through my old ideas and seeing which ones are worth using and I'm a bit conflicted about one of them. The idea in question involves a character who is sort-of possessed by a non-too-bright entity of some sort which needs a host to survive. On the bright side, it makes an effort to keep its 'home' in good repair and the host is usually in charge, but on the down side the character gets kicked out of the driving seat from time to time. The thing I'm having trouble with is working out how the host got possessed in the first place (I did have an idea but it ended up being rather convoluted and stupid so I'm ditching it). Any ideas?

Well, what sort of entity is it and what is its usual lifecycle?

It's non-corporal and as for a life-cycle, I don't think it has one. One thing I'm keeping from my original plan is that whatever it is, it's old, as in Time Abyss old.

Is it usual for this entity to possess others? Can you tell us more about its nature?

One thought that comes to me is a curse: the entity was trapped in an amulet, and a curse placed upon that amulet such that whoever picked it up would be possessed by the entity. As for why that particular entity, perhaps its low intelligence resulted in it being considered a burden, and thus a potential punishment, or perhaps it was selected by mistake, or the punishment was for the entity more than the host.

Hmm, interesting idea. I'll consider it.

As for the entity, as I said before it's non-corporal and always has been. While that may be fine for it wherever it comes from, in this world it needs a host body in order to survive and/or function. Body surfing isn't really possible since some very specific circumstances are required (in my original idea, it was working it's way down a particular family line but that idea ended up resulting in too much fridge logic). Alignment wise, it's pretty much neutral. As I said before, it doesn't seem to be exactly sapient. All it seems to really care about is its survival, which by extension means its host's survival, and going by the amount of effort it puts into keeping its host in tip-top condition, it seems to prefer a fully functional, healthy body. However, it's generally just a 'passenger' rather then in control, well most of the time. My original idea had it linked to its host's fight-or-flight response in some way; if the host got terrified enough, they went bye-bye and the entity took over to do whatever was necessary to keep them alive. Emphasis on 'whatever was necessary', it only cares about it's own survival and that of its host and it can fix pretty much any damage the host sustains provided that it's not enough to kill them, plus as I've already said, it's not all that intelligent. In the story I wrote prior to fridge logic setting in and making me shelve the idea, the host only became aware that they weren't alone in their body after something happened to trigger the above scenario. It was very unpleasant.