Exactly the same as any commodity price in the world falls and rise. The law of supply and demand. It never goes out of fashion, does it?
The price of a bitcoin is tied purely to the laws of supply and demand. In other words, the price is determined only by what the market contributors are willing to pay. If more people want to buy bitcoins, then the price will increase. If more people want to sell, the price will decrease. That’s how it works. Pretty much the same?
But why does it fall and rise so often? or why is so much volatile?
Boom - More and more people are finding out about it and they want’s their hands full.
Relatively small market size - Bitcoin’s value can be volatile when compared to more established currencies and commodities. This can be attributed to its relatively small market size, and it means that a smaller amount of money can move the Bitcoin price more significantly. This discrepancy will decrease naturally over time as the currency matures and the market size increases.
There are many other factors involved but I guess these are the important ones.