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I read this question on money.stackexchange, in which a user asks how to tax the speculation gain they (involuntarily) made. This guy (or girl) bought BTC for a few hundred USD a few years ago, lost the respective harddrive, and when they found it again, the BTC were (supposedly) worth a million or so USD.

So I am wondering, why did BTC appreciate so dramatically in other currencies? Is it just because of rising demand, in turn due to increasing trust in BTC?

As a corollary, could the BTC appreciation also be driven by a speculative bubble?

Sorry if this is a very noob question.