If you assume markets are efficient—and that miners will always point their hash rate to whoever bids the highest—then no amount of block reward actually guarantees security. Even if it costs 1 billion of hashrate and energy to attack, the attacker also earns 1 billion in block rewards from the attack. So the net cost could be close to zero—effectively free. That’s why the idea that “higher block reward = more security” doesn’t hold up under these assumptions. So what actually keeps the system safe? Double-spend counterattacks. If someone tries to attack and double-spend coins, the victim—like an exchange—can retaliate by launching a counterattack. They rent hashrate, rewrite the blockchain, and reverse the attacker’s transaction. That threat of retaliation makes the economics of the original attack much worse. The attacker may lose everything. And knowing that, they often don’t attack at all. This isn't just theory. We've seen it play out on smaller proof-of-work chains. Attacks have happened, but there’s a retaliation, and it ultimately creates a no-attack equilibrium. And over time, even with very small block rewards, these chains often go long periods without any attacks. Because once retaliation is credible, the first attack becomes too risky.