Difficulty

Difficulty is the network's thermostat: more hashrate joins, blocks come too fast, difficulty rises until the target block time is restored. Bitcoin adjusts every 2,016 blocks (~2 weeks); Litecoin every 3.5 days; Bitcoin Cash recalculates every block via ASERT; Monero and Kaspa continuously.

For miners, difficulty is the silent competitor: your hardware's share of rewards erodes as global hashrate grows, even when coin price is flat. Profitability projections that ignore difficulty growth overstate earnings badly — stress-test at +20–50% annual growth.