these “things” that exist on the blockchain are sometimes representations of ownership (think like a deed for property: it’s just a piece of paper that represents ownership. that could easily exist on the blockchain, where the owner of the property is the person who is assigned the deed on-chain)… the you can have a smart contract that automatically releases funds to the seller once the deed has been transferred to the buyer
The idea that property can be accurately recorded on a neutral blockchain is absolutely ludicrous. What happens when the owner of the property dies and they are unable to update the record? What if there is a dispute among the heirs? What if the owner goes bankrupt and their assets are seized by a third-party, but they are still unwilling to update the blockchain record? There is a reason that definitive records for real property are maintained by the government itself. Anything of real value must exist within a legal framework and be subject to a change of ownership under law or court order.
If a judge determines a property belongs to someone else, the sheriff who comes to evict you isn’t going to care when you point to some record on a blockchain. If a blockchain record can’t be unilaterally updated by the government to change ownership, against the wishes of the current owner, then it cannot function as a true record. Consequently, any “smart” contract based on that record is unreliable as well since the seller may not actually own in the real world the thing their blockchain deed says they own.