I'm working on a project creating fun online tools for kids. One thing I noticed immediately in usability evaluations was that kids don't read anything. They just charge forward clicking buttons and trying stuff out, until they get stuck and give up. If only they would read the directions first! Then they would know how to use the tools correctly. No trial and error would be necessary.
The paradox of the active user is a great description of this common behavior. Because people use software to get something done, they tend to immediately begin working towards those goals as soon as possible. As Carroll and Rosson put it, "the typical pattern we have observed is that people simply strike out into the unknown." The paradox is that in some cases, people would finish tasks faster (and with less frustration) if they weren't so quick to get started.
Usability professionals must design for people who don't RTFM by putting instructions in context. At the left is a link for a subset of the current MSN registration page. Instead of text exhorting the user to "make your password difficult to guess," or errors that pop up, MSN turns password creation into a game with their password strength meter.