I noticed that the price of Bitcoin change much like all altcoins.
But the price of other traditional currencies like the euro, for example, are stable and do not change much.
It is the government that control their prices?
Besides government controling fiat currency price thers is also other reasons of bitcoin price instability.
Bitcoin is relatively new and has limited supply.When new users adopt bitcoin, it creates it's demand and hence price goes up.
Bitcoin is truly global : unlike Euro,dollar etc bitcoin is not restricted to international boundaries and this is also one of the reasons why bitcoin price fluctuates frequently.