Mining pools
The individual odds of winning the reward for adding a block to the block chain decrease alongside an increase in the number of miners. Many miners participate, but the reward for each block can only go to a single bitcoin address. As of 2014 it has become common for miners to join organized mining pools,[28] which split the work and the reward among all participants and make mining a less risky endeavor. Even for those who join pools, the cost of the electricity necessary to mine may outweigh the bitcoin rewards from doing so