A blockchain is a closed virtual world proving only claims about itself

For example, a transaction may contain proof that the private key associated to the address mentioned in a previous transaction has signed this new transaction.

A blockchain is an axiomatic system with a growing list of proofs. Each transaction accepted to the blockchain is a new proof. About existing proofs, you can derive new proofs.

A proof is a claim for which all untruth can only originate from the untruth in the underlying axioms.

It is pointless to try to use a blockchain to prove anything about the real world, because proving anything about the real world is fundamentally impossible.

Some people simply refuse to graduate to the understanding that proof is only possible for an abstract world for which you can provided the complete construction logic, i.e. its axioms.

You cannot provide the construction logic of the real world, because you did not build the real world by yourself.

For example, a blockchain is absolutely not usable for KYC ("Know Your Customer") or AML ("Anti Money Laundry").

In the real world you cannot prove that John is John. He may say that he is John, and he could provide some paperwork that seems to say that too, but all of that does not prove anything.

We generally assume that the cost to fabricate the documentation somehow exceeds the benefits of doing so. Still, the internet has drastically cut down on the cost of fabricating any possible piece of information.

President Obama could not prove that he was born in Hawai, if only, because such proof cannot possibly exist. Imagine that you personally saw a baby in the hospital back then. On what grounds can you insist today that it is the same Obama?