Advanced Persistent Threat (APT) attackers accomplish their attack objectives by co-opting users' credentials. Traditional cyber defenses leave users vulnerable to APT attacks which employ spearphishing. The success of spearphishing attacks is not a data processing failure, but is the result of defenders failing to apply the principles of Human System Integration to the problem of spearphishing. We discuss an alternative defensive strategy which addresses human performance capabilities and limitations to disrupt spearphishing attacks.