In other words: in classic PoW attacker needs to spend money on the attack, and if attack fails, they get nothing in return, they just wasted money. If PoW prot

In other words: in classic PoW attacker needs to spend money on the attack, and if attack fails, they get nothing in return, they just wasted money. If PoW protocol is doing some useful work, then attacker can also benefit from that work, which means the cost of failed attack goes down to almost zero.