From the usability bible, now revisited:

1. Users don’t read, they scan pages.
2. Users take decisions based on trial and error. If they don’t get what they expect, they hit the ‘Back’ button; there is no penalty for being wrong.
3. Users are in hurry; they don’t read instructions. They don’t really care how the things suppose to work; if they find a way that works, they stick to it.

Image: Disney