Banks and trading houses are kind of the exception in that regard. I pay my bank monthly for my mortgage, and thus I live in a house that the bank could repossess if they so choose.
The phrase really should be about force rather than possession. Possession only really makes a difference when there's no power imbalance.
Banks have the legal authority to take the home I possess if I don't meet the terms of our contract. Hell, I may own my property outright but the government can still claim eminent domain and take it from me anyway.
Among equals, possession may matter. When one side can force you to comply, possession really is only a sign that the one with power is currently letting you keep it.
Absolutely not. You are protected my law, regardless of whatever odious mortgage contract that you signed.
What is about HN that makes so many commenters incredibly distrustful of our modern finance system? It is tiring, and they rarely (never?) offer any sound evidence to the matter. Post GFC, it is working very well.
Possession is 90% of ownership