In short: Stablecoins stay stable because every digital unit is matched by real money - verified, audited, and redeemable at any time.
How are stablecoins kept at $1 / €1?
Each stablecoin is fully backed by real assets, usually cash or short-term government bonds.
1 digital € = 1 real € held safely in reserve.
When people buy, the same amount of real money is deposited and stored by the issuer.
When people sell, the issuer returns the money and destroys the corresponding stablecoin - keeping the balance at 1:1.

