Almost everyone who encounters the idea for the first time (including me) has the same reaction, that can't possibly work. But so far the market has proved the skeptics wrong.
The currency you are most likely used to right now is fiat money or in other words "imaginary".
DEFINITION OF 'FIAT MONEY'
Currency that a government has declared to be legal tender, but is not backed by a physical commodity. The value of fiat money is derived from the relationship between supply and demand rather than the value of the material that the money is made of. Historically, most currencies were based on physical commodities such as gold or silver, but fiat money is based solely on faith. Fiat is the Latin word for "it shall be". http://www.investopedia.com/terms/f/fiatmoney.asp
So I would ask you, why do you use an imaginary currency?