It goes up a lot when it gets a ton of press, because saturation level (knowledge of existence) amongst the 'average' investor is still low.  Additionally, the number of people rubbishing it as a joke continues to drop. 

Random people invest in it, w/o regard to the price, since they see a nice chart and don't want to miss out.  This has happened.... at least three times in the past, maybe four.  One of the other massive runs was when MtGox was manipulating the price.

I sold half of mine at $36,500.  I was thinking I'd be able to rebuy at ~$18,500 level, ~$22,500 level, or around the 50 day MA when I sold (at the time it was ~$24,500). 

It appears that someone wants to keep it above $30,500'ish, which is actually close to the 50 day moving average now (think it's around $29,500).  There was that 'flash crash' down to $29,000, but it immediately went back up.  If it holds the $30,500 - $31,000 for another week or two, I may cave and re-buy at this $31,000 or so.  Probably not, though.  I still think the price is massively inflated.

But I guess with virtually every govt going massively into debt and the Federal Reserve printing untold amounts of "funny money" to keep the US stock market from crashing, who knows. 

I'm unsure why we aren't already seeing massive inflation in the US.  Probably the low cost of energy has cancelled out a lot of it.  This low cost of gas and such shouldn't last too much longer w/ Beijing Biden.  China needs to sell some solar panels.