Here’s a simple truth when it comes to security, courtesy of Bruce Schneier:

Security systems fail in one of two ways. They can fail to stop the bad guy, and they can mistakenly stop the good guy. The TSA likes to measure its success by looking at the forbidden items they have prevented from being carried onto aircraft, but that’s wrong. Every time the TSA takes a pocketknife from an innocent person, that’s a security failure. It’s a false alarm. The system has prevented access where no prevention was required.

Everyone working in security knows that the first case is a failure, it seems like almost noone sees the second case that way.