After a long time bitcoin gone under 10000$ 
and crypto market down also.What is the main cause? bitcoin ban facebook ad or other option ??
It could be one reason why we see the price of bitcoin suddenly goes down below and stuck at $9300. We can't say for certain what is the main cause of the sudden drop of today's price. There might be FUD around that I'm not aware of. Its really annoying and frustrating to see the price not making any headway to the direction that we wanted to, the only thing we can do is really wait. and crypto market down also.What is the main cause? bitcoin ban facebook ad or other option ??My personal view says that around mid-Feb we will on the road to recover. And in this kind of scenario, you better just hold into your bitcoin and don't just panic sells.
It is down to $9100 today. I think the FUDs did played a part. I mean just look here in the forum, everyone's talking about ICO restrictions in South Korea. Not as often talked about is India's current stance.
I think some people also ended up taking out their money during the peak last year. Probably even those that have just bought tried to sell when they saw it falling.