As a day trader in both crypto and equity, let me tell you this, we are betting that we can get rid of whatever we buy at a higher price in the least amount of time.  We can limit our risk with stop loss, options and ...... but ultimately we are buying low and selling high.  That's all, there is not secret formula or advance knowledge for 95% of us, and the other 5% will have SEC knocking at the the door..... What we know as day traders is excatly as what you know, but it is our experience that makes us different.  Crypto has a lower entry level(around 5k) compare to most exchanges, in US the minimum is 25k capital (yes, you can do 10k for a regular margin account, but PDT is a pain to avoid), so your losses are minimal.  

Let me put in a other way, sometimes people  will preceive it wrong when they sell something. 

Will you take out a mortgage on your house to buy bitcoins?
If the answer is yes, then don't sell your coins, otherwise you should consider selling it. 

Note:  Shorting equity in a house is dual(opposite) transaction of paying off a loan, so the calculations should be in theory should be the same.  A human bring is a strange thing, and the notion of buying and selling affects it.   

Unless china does DPI and intercept every bitcoin operation, how can China  "Ban" bitcoin?  Didn't China just only shutdown exchanges?

I am just wondering what are the current of definition for invest in this topic?

It is like gold, you don't invest in gold , you speculate... bitcoins in terms of factors of production is worst then gold.