The attitude of the government and the law to Bitcoin has a great influence on this.
Hacking (hacking), although this is not a definitive factor, once Bitcoin is stolen, especially at a certain exchange, many Bitcoin players lose confidence in Bitcoin and form a sell-off.
There's a big factor that affect to the bitcoin price if people are lack of knowledge through cryptocurrency and they really don't believe that the bitcoin will never be crash. Panic selling is one of the factors that affect to the bitcoin price. They do panic selling because they are afraid that the bitcoin will going to crash. The negative news and FUD that poisoned the mind of the people to do panic selling and dumping the bitcoin price.
For me, the factors that affects the value of bitcoin is determined by the demand and supply by the investors. The continuous threats of hackers of bitcoin will definetely change it's value in the market.