Repeated behaviours

Why is it that we do things we know are really not a great idea? Why is it we do them again and again?

For instance, the other night I was about to go out, but I quickly wanted to check my email. I switched on my PC, and then was told there was some Microsoft update that needed to be installed. Instead of NOT installing it, because I really only had ten minutes before I had to leave my flat, I went ahead and hit Install. Even though I knew, deep down, that there was a snowball's chance in hell of the install completing before I had to leave.

So, of course, it took ages & ages, and I ended up leaving my PC on while I was out, which I try not to do so as to save electricity and thereby - albeit indirectly - the planet.