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A simple thought experiment can show that if Satoshi had kept all 21 million Bitcoins to himself and never shared this idea with anyone, the value of Bitcoin would be zero.
discuss
That makes sense because something of value is measured by its features, usability, demand and rarity. So when Satoshi introduced Bitcoin to the public, that's where the public will evaluate Bitcoin, whether it's worth it or not, it turns out that the market response was very good to the presence of Bitcoin and the price of Bitcoin began to increase.
And moreover, if only Satoshi had not made Bitcoin public, not only would the value of Bitcoin be zero, but also the cryptocurrency market would not exist and we would have no alternative for our transactions.