lately,the bitcoin price has been go down ,why? what happen important event
Because somebody is pumping and dumping. Or rather, just mainly dumping when the price reaches a certain threshold driven by legitimate buyers. If you analyze the volume it is really interesting. When bitcoin reached 11~12 recently, it got there with relatively low volume (ligitimate users buying the commodity). Then the dumper strikes and the volume spikes like crazy. The dumper stops just before causing a crisis, then patiently waits until the market self heals again and repeats the process.
I attribute this to people with a lot of bitcoins cashing out in an ordered manner to get the most for their money. People by the way, that clearly do not care about the bitcoin economy, but purely about their own greed.
Why do you class buying as legitimate but selling as somehow malevolent? Could the sellers not just be miners trying to pay their electricity bills? I mean in the context of 5k bitcoins being mined every day, the 5k dumps you see on MtGOX every fortnight or so are really not large at all..it's just one day's worth of mining. Or 3% of one month's mining.
In any case, if these people had cashed out in April when we were at the same levels as we are now, bitcoin would never have reached $30, we wouldn't have had the big crash, bitcoin would have been far less volatile and everyone would have been happy. So would that have been evil in your PoV? As in all markets, cashing out at the right time reduces overall volatility - calling it 'greed' is just childish.