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There's the greater fools theory. People are happy to spend $100k on something that they believe they can turn around and resell for $150k in a month.

There's also an anchor effect from loss aversion. If I bought a crypto-cat for 1 Ether, and then Ether price increase by 300%, I might refuse to sell the crypto-cat for less than 1 Ether, even though there's no intrinsic reason for my cat to appreciate at the same rate as the base currency.