Staking yields are paid in the token itself, so a 4% yield on a token that falls 30% is still a loss in dollar terms. Lockups can prevent selling for days or weeks, and validators can be penalized (slashed).
Exchanges and liquid-staking protocols simplify it but add counterparty or smart-contract risk.
Example: staking 10 ETH at 3.5% earns about 0.35 ETH per year. If ETH falls from $3,000 to $2,000 over that year, the position is worth $20,700, down from $30,000.
Related: defi, wallet, on-chain, stablecoin