Difficulty Adjustment
Difficulty adjustment automatically tunes how hard the mining puzzle is so blocks keep arriving at the intended pace.
In depth
Bitcoin targets one block every ten minutes. Every 2016 blocks (about two weeks) the protocol checks how fast blocks actually came and raises or lowers the target accordingly. More miners joining does not speed up the chain — it just makes each block harder to find.
Why it matters
It keeps issuance predictable regardless of how much hardware is thrown at the network.