How people buy and sell is one of the reasons that make the price to change often, when people buy much the price will go up and when price go down it means people are selling.
In addition to demand and supply there are several factors that make up bitcoin prices, such as the importance of protecting the value, the price of a bitcoin trading contract and so on. The perception factor also affects the price of Bitcoin. If Bitcoin gets a better perception, demand for Bitcoin will increase. Followed by the rising price of Bitcoin. Conversely, if Bitcoin gets a poor perception, the price of Bitcoin will decrease.