Computer "Security"

I recently bought a security cable for my laptop, so that I don't have to take it with me every time I go to the bathroom or to get coffee when I'm doing homework on it in a public space.
The first time I used the cable, I was feeling all smug and happy with myself. I locked the computer to the desk, and thought "okay, I can leave my handbag here, there's nothing *that* valuable in it (just my wallet, but not that much cash, definitely not as attractive a target as a laptop).
I came back after a while, and as I was getting ready to get back to work, I realized the handbag contained my keys, including the key to the laptop...

I think this is highly symbolic of they way security works in the real world. "It is not security, but the appearance of security, that matters."