The problem is that you can't actually be secure. This applies in all real situations. You can, however, be secure enough (ie. you achieve your security goals),

The problem is that you can't actually be secure. This applies in all real situations. You can, however, be secure enough (ie. you achieve your security goals), with some thought and planning. There is a difference though. What is expected when you go through airport security is that you will be "secure", ie. absolutely secure. The problem is that this is impossible. There are a myriad of ways that a person can cause untold mayhem in what is arguably one of the safest modern forms of long distance travel. Due to this impossibility, you see the authorities forever imposing tighter and tighter safeguards without any real improvement to safety. What is done, however, is "secure enough", ie. it achieves the required security objectives (chance of serious injury/death is negligible, chance of being able to hijack a plane is negligible, etc.). This then leads to a problem when "secure enough" is not "completely secure" in a way that didn't lead to a failure in a security objective. Then you have political pressure to "tighten up security", with no actual need, thus you have what can only be termed "make work" programs that look reasonable but do basically nothing for security.