You can put the following information on blockchain: "1+1=5", and in that way prevent it from being changed. But that doesn't mean one plus one equals five. It's false information. The same is true with bitcoin blockchain. Nakamoto's software writes false information into that database. According to this information, address holders have a specific amount of bitcoins, coins, tokens, asset, digital commodity, or whatever one calls that supposed digital resource. Yet, nobody is able to show that resource.