Security. Lots of computer system companies are selling security these days. Ironic, when you think about it, because computer systems are systems, and systems are inherently, well, vulnerable. Not secure.
It's a feature of systems, even though systems designers from the times of the earliest recorded history have habitually insisted their systems are somehow different. (Vulnerability is not just a feature of mechanical systems.)
Security in the usual sense is a red herring, a distraction.
But if you want security, here are the two principal keys:
Know who you are and where you are.
Know what is most important and where it is.
If you don't know the above, what use is building walls?
If you do know the above, chances are you'll have little use for walls. Just enough to keep other people from getting worried.
This all sounds ridiculous, but it has practical application in computer and information science. Systems must understand identity at some level to be secure.
Which begs the question, what is identity?