So basically it depends on the growth of the particular currency. The more it develops the more it's prices will increase.
And also you can watch the graph and watch how it has grown over the years.
Like I know why you wanted to ask this question , as you want to buy bitcoins and sell them when the prices rise again.
But mostly you can predict without knowing much. For eg if the prices rise too much ,
Then the people will sell their bitcoins which would lead for the prices to fall.
Then people will buy more bitcoins and then it will increase. This process keeps continuing.
I agree, but partialy, because Bitcoin price doesn't depend exclusively on the supply and demand. There are also other factors on the market and you can't exclude the situation in China too. So, no matter how easy and logical it seems and looks you have to calculate all available information but still you could go wrong.