Often "the Thing" turns out to be when one does something that empowers them and gives them a sense of accomplishment for self and someone else devalues it or behaves in a way that turns it into something negative. This tends to be something that triggers ptsd symptoms when someone struggles with ptsd. And if it's cptsd, it can go way back for someone to something that person experienced in their childhood growing up.

The fact that you don't even want the truck now tells me that it's not so much the truck but that you were so happy when you got it and someone else ruined that for you. So, it's the feeling of that itself that you want no part of.

Does that describe the "Thing"?