When more hashrate joins a network, blocks would arrive too quickly, so the protocol raises difficulty. When hashrate leaves, difficulty falls. Bitcoin readjusts roughly every two weeks; other chains adjust on different schedules.
Difficulty is the quiet antagonist of mining economics. Your hardware is fixed from the day you buy it, but difficulty generally rises, so the same machine earns less over time even though nothing about it has changed.
This definition is educational and not financial advice. Crypto is volatile and high-risk — always do your own research.
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