Machines built for one job
In 2009 a normal computer processor could find blocks. Graphics cards took over in 2010, then from 2013 ASICs: chips designed only to compute Bitcoin's double SHA-256, millions of times more efficient than a laptop. Mining with anything else today wastes electricity.
Pools smooth the luck
Even with a good ASIC, a lone miner might wait years for a block. A pool groups thousands of miners, gives them work, and shares each block's reward according to the work each one contributed. The income becomes small but regular.
The pool chooses which transactions go into the block template, which is why pool concentration is watched closely. But the pool does not own the machines: if a pool misbehaves, miners can point their hashrate to another one in minutes, and they have done so in the past. Newer protocols also let miners build their own templates.
▶ SEE IT IN THE MACHINEAround the MINING bench stand 23 machines of every size: a big farm, a medium workshop, a garage, all hashing for the same lottery.