Choice.

Joel Spolsky explains what's wrong with Microsoft's interface design — and, come to that, what's wrong with most interface design, and not just in the IT world:

I'm sure there's a whole team of UI designers, programmers, and testers who worked very hard on the OFF button in Windows Vista, but seriously, is this the best you could come up with?

Every time you want to leave your computer, you have to choose between nine, count them, nine options: two icons and seven menu items. ...

On many laptops, there are also four FN+Key combinations to power off, hibernate, sleep, etc. That brings us up to 13 choices, and, oh, yeah, there's an on-off button, 14, and you can close the lid, 15. A total of fifteen different ways to shut down a laptop that you're expected to choose from.

The more choices you give people, the harder it is for them to choose, and the unhappier they'll feel.

Joel goes on to explain his own solution to the problem. It is extremely good, and Microsoft, and every other company in the world, should use it.