I just want to share a paragraph on the general rule on why Bitcoin price goes down and up. From this website https://www.cryptocoinsnews.com/bitcoin-price-falls-300/
Although this basic principle is not new, but hope it helps others. So knowing this fact, why are people selling Bitcoin yesterday and today, and kept on selling? Who sold it? We know that ESPN sold over $500,000 (USD) of Bitcoin , yes that will have an impact on Bitcoin, sad thing is nobody is buying. So who else are selling these Bitcoin causing the price to plunged to below $280 now? Could it be those that won the government auction of Bitcoin? Could it be the mtGOX hacker or MtGOX staff themselves emptying their Bitcoin wallet due to the investigation now at MtGOX aim at it own staff members whom might be stealing hiding the bitcoins?
As CCN observed in September, use drives down price. If everyone wants to buy and nobody wants to sell, the price skyrockets. If more people want to sell, the price goes down. This basic principle of economy applies to everything, including Bitcoin.
Today we have a critical mass of people who use their bitcoins to buy goods and services. We pay merchants in Bitcoin, and sometimes they use bitcoins to pay their suppliers, but at some point in the chain somebody will convert the bitcoins to fiat currency, and that will pull the value of Bitcoin down.