This is why I love security so much. You have to continually challenge the assumptions that underlie most people's thinking. For example almost all consumer locks can be picked within 30 seconds. Home alarm devices can be defeated by a quick team, a sledge hammer, a mask, and a car. The most secure systems have been taken down by attacking the email of the security chief's wife. Attackers are bold, they are creative, and they always keep you on your toes. It only takes one tiny opening for an attack to be put into play, and that opening more often than not is just a small stupid little thing that you failed to consider. Things that people don't seem to consider include the personal security of their employees, a USB stick being passed around air gap SCADA systems, or their ability to deal with multiple attacks simultaneously.
It only takes one flaw to bring an entire complex system to its knees. It takes a whole lot of challenging faulty abstractions, critical thinking, extreme pessimism and a whole dollop of both cynicism and pragmatism to keep them purring along.
Security rocks. Only the paranoid survive.