Say you are on a desert island with one other person. You have some possessions, and I have some possessions. Perhaps I have a locket, with a photo of myself and family inside. One day, I go off to fish, leaving my precious locket behind. I never come back - eaten by a shark.
You are now alone. My stuff is no longer “mine” in any sense, as I am now gone. And without possession there is no moral or social guardrail of theft. It is just stuff, that is there to be used. Maybe the chain of the locket can be used to hold a bucket over a fire. The logical question for you to ask is “How can I use this stuff to stay alive.”
But, this is not the only way of looking at things. You could also look at it spiritually or sentimentally and bury the locket.
Connections
Instrumental Reasoning Is a Symptom of First-Principals Thinking