In Proof of Stake, the "nothing at stake" problem is prevented by requiring validators to commit their cryptocurrency as a stake in the network. Validators are economically incentivized to act honestly and follow the consensus protocol, as they have something to lose if they misbehave. This financial commitment helps secure the network and discourages validators from supporting conflicting or invalid blocks. Additionally, protocols like punishment mechanisms and slashing can be implemented to penalize validators who attempt to act maliciously.
