Most security systems have the annoying side effect that increasing attack volumes can degrade them, usually through tuning of defenses, or desensitization (Yes, this is a generalization). Social Engineering, on the other hand, has the nice feature that the more often someone tries to social engineer you, the less likely the next person is to succeed - even if the first attack is incompetent, and the second one highly competent.

That's because every failed attempt is a training exercise for the target.