When you unstake, most proof-of-stake networks don't return your tokens immediately. Instead, they enter an 'unbonding' or 'undelegation' period — anywhere from a few hours (Solana, Sui) to 28 days (Polkadot) — during which your tokens are locked, earn no further rewards, and cannot be transferred or sold.
This delay exists for security reasons: it gives the network time to detect and penalize misbehavior that occurred before you started unstaking, and it prevents an attacker from quickly staking, attacking the network, and exiting before being caught. The length of the unbonding period is usually a deliberate protocol design choice balancing security against staker convenience.
Liquid staking tokens exist partly to work around this constraint — instead of waiting out the unbonding period, you can sell the liquid token on the open market immediately, though usually at a small discount reflecting the time value of the underlying unbonding period and prevailing market liquidity.
Always check a specific network's current unbonding period before staking a meaningful amount, since these parameters can change through governance votes over a chain's lifetime.