If you use a local wallet to store your BTC, let’s say on a HDD, the the magnetic pattern on the disk that makes up the bits that represent your coins would be physically owning then. They can’t be retrieved any other way.
Still, access isn't really possession is it. I can lend my house key to a friend but they don't possess my house. The deed is what really declares me the owner. In the case of your coins, it's the consensus of the blockchain.
Not all discussions require the highest level of technical detail.
But if you have a $100 in your bank account, there is an additional constraint – you can spend it only if your bank is alive and functioning correctly and lets you specifically (you are not sanctioned/banned) to spend it.
Same is the case with bitcoin for those who store their private key on exchanges.
First there should exist a market for it (others who also believe bitcoin has value). Then, just like banks, the bitcoin exchanges where you escrowed your key have to let you spend it through them.
If all exchanges you have access to in your country decide to ban you (because your govt told them to) then you cannot spend your bitcoin.
In this way, bitcoin and your bank account balance are similar and they both are different from hard cash in hand or gold coin in hand.
If you hold your private key yourself and run your own bitcoin lightweight node to connect to bitcoin network and submit your transactions, then you don't need exchanges. Even then, others who use exchanges maybe blocked from transacting with you through govt sanctions etc.
Given my bank is on the list of "systemically important banks", if it goes under/down there's probably more going on in the world such that I probably won't be worrying about my proverbial $100 too much:
* https://en.wikipedia.org/wiki/List_of_systemically_important...
(And I do have accounts at multiple banks in case of IT problems at one bank.)
> If all exchanges you have access to in your country decide to ban you (because your govt told them to) then you cannot spend your bitcoin.
Of all the things that I could worry about going wrong in my life, these doomsday scenarios are not even in the Top 1000. I'm more worried about stubbing my toe than some of these currency collapse scenarios that some Bitcoin fans come up with.
You can think of Bitcoin as a kind of identity management system. The blockchain stores transactions mapping public keys to each other and monetary values. As long as you remember the private key matching your public key you can issue transactions on the blockchain.
Contrary to common belief Bitcoin is not stored on your hard drive, they contain only your private keys. The monetary units themselves, “UTXOs”, are stored on the network of Bitcoin nodes distributed all over the world.