For other factors such as :
Goverment Policy: if goverment accept bitcoin as legal payment, the value might be increase
I know that's pretty logic , people will wonder what Bitcoin is from curiousity and end up using it at the end and since Goverment is allowing it and using it then people will buy more and more (more demand) => rise price . I understand that .
If there is a market (enough buy and sell orders) then the price will be determined by supply and demand.
Between exchanges (and other places where buying or selling takes place) there is some amount of arbitrage (when you can buy BTC at one exchange for $285 and can sell them at another exchange for $295, some folks will buy on one exchange and sell on the other, adjusting supply, demand and prices on both exchanges.)
Without markets, determining a price is difficult. Remember the classic bitcoin pizza? At that time, a future price of $1 per Bitcoin was considered pretty much impossible, so Bitcoin was valued much less than that. Later on, when it became clear that you could not only buy pizza with BTC, people were gradually willing to value it more.
Onkel Paul
the pizza example makes sense and it's a very good example to explain things
highlly appreciate your help man