The core conceit that people gloss over is the fact there is no such thing as a "wallet" that "stores" bitcoins. The only thing that exists is a public record of numbers saying they're giving bitcoins to other numbers.
When you create a "wallet", you're choosing a private number that nobody knows and nobody has already picked. You use this private number to create another number, the public number, the "wallet address".
Since this number doesn't exist anywhere in the public record, we say you have "zero bitcoins."
Then, you get someone to claim "I am giving x bitcoins to your number". If you can get this claim (a transaction) into the public record (the blockchain), we all decide to agree "This happened." And now we say you have x bitcoins. Why? Because now you're allowed to make a transaction saying you're giving those bitcoins to another number!
It's all made up. This is what currency is, it only exists because of collective trust.