What you're really asking is "does anyone think that $19k for Bitcoin is undervalued?" And there are certainly people who think that.

So what is the fair value of Bitcoin? Well, it's a new economic idea [1], so there's not a lot of prior art to gauge here. There's no P/E ratio, no rent/price ratios, nothing of that sort to give you at least a baseline feel for "does this seem frothy?"

Indeed, its value is ultimately based on projection: whatever you think Bitcoin could do, what values it might have, that's the valuation you're going to give to it. And people have given really daft ideas of its value: I've seen someone seriously argue that Bitcoin is useful for people who lack phones or internet. Other people argue that $19k is cheap, if Bitcoin somehow replaced all fiat currency. So there's no shortage of people willing to bid prices higher, and that's not counting speculators hoping to make money on a "free" get-rich-quick scheme.

[1] I say this as someone skeptical of high valuations of Bitcoin. Just because something is new and transformative doesn't mean it's valuable--just ask CDOs.

A lot of people? People continued to buy all the way up to 19.5. The thing about Bitcoin is, almost everyone expected a drop, no one knew when or how high it would go before it dropped... or how far it will drop.

Everyone also expected it to drop at 5k, 10, 15k and it just didn't happen to a large extent. I stupidly bought in at 10k and got lucky to make some money but others stupidly bought in at 20k.

The only thing definitive about Bitcoin is that it will go up..and down. Claiming to know how high, how fast, or how low is BS.

One of the infuriating things about Bitcoin is that there's no reason 19K couldn't be the new normal. You don't have to trade in whole Bitcoins, so high prices just mean people trade in smaller fractions and low prices just mean people trade in higher numbers, unlike a stock where you might want to do a split to make it easier for people to invest.

I wanted to short bitcoin, I predicted a price correction of -50% after the CBOE and CME futures came online, and well, here we are. Unfortunately I can't post 200% margin even on a 20k contract :(

edit: The futures markets may not have even been the catalyst for this drop, more likely it's this: "The market has also been artificially pumped up by Bitfinex and their money printing machine Tether."

Is there really much there is to expect though? Bitcoin's value has no real basis one way or another, since all the purported practical uses have fizzled out once the network became incapable of actual commerce due to various factors like transaction fees, price instability, processing delays, etc.

So I guess by now, Bitcoin crashing by 50% is as surprising or unsurprising as Bitcoin growing by 50% instead. So I'm not sure if you could really expect the crash, since that expectation requires understanding the unknown speculation mechanism that currently drives it. Though in the future some analysis in hindsight might tell us how to explain what market psychology is currently influencing the price.

Some expected the 19k last week will go to the moon. Haha

Can you explain why is 19K less normal than 500K or 100$?

Yes. https://news.ycombinator.com/item?id=15984381 (This commenter at least hedges at the end, but this kind of reasoning could be found all over the relevant sub-reddits and other corners of the internet this week. Every bubble has a "this time it's different" motivated-reasoning thing...)

Edit: Here's another from the same thread, with a motivated response to "sell when the shoe shine boy gives stock tips" on why "this time that's different" https://news.ycombinator.com/item?id=15983811