What are the motivations of the tarnished? [Question]

I get what we're trying to do. "restore the elden ring" for whatever reason. but there are a few things I'm a bit unclear about. namely.... why? from what I know the elden ring is an item of great power. "destroyer of worlds" sorta thing. and the tarnished is tracking down fellas with parts of the ring (great runes) and taking it for themself, in an effort to become the elden lord. the one and only thing I don't understand about this, is why is the tarnished doing all of this? to my knowledge they're like regular people with the ability to see the grace of the erd tree, and come back to life. to my knowledge they're not forced to follow the grace of the erd tree (hence why there's still a good bunch of them outside the lands between according to "joe the internet guy who may or may not be correct in their assessment of the lore") and even if they were that doesn't directly corelate to the ring.

granted, I got some of this info from "joe the internet guy", so some of this might be off and anything that is, please do correct me where I'm wrong. just a bit curious on the side of why are we doing what we're doing, and figure this place is a better place to ask that question than the alternative (chat gpt. that thing did give me an answer but it's replies in the past have been suspect at best and google was no help)

EDIT: typo's/fixed phrasing