The main reason for the volatility of Bitcoin is simply because it's a decentralised digital currency,which means it's not regulated by the government.
not only that, I think supply and demands are also very influential on bitcoin volatility. quite reasonable if demands rise then the price will rise. while when demands down, then the price will also fall. and I'm sure demands on bitcoin are also unstable, surely people who pick bitcoin will always sell when prices look up and buy when prices go down. unstable continue to buy or continue to sell.