http://www.coindesk.com/top-10-bitcoin-myths-debunked/Bitcoins are validated through blockchains, which are ledgers of past transactions. Miners who process and verify Bitcoin transactions are rewarded with bitcoins, as well as with fees others pay. Like the saying goes, it costs money to make money and, to date, mining bitcoins has cost hundreds of thousands of dollars. This design is intentional: the difficulty of mining is built in to limit the number of bitcoins found each day. In addition, there’s a hard limit on the number of bitcoins that can be mined: 21 million coins, which is expected to be reached by 2140.
