Timoni West is a web designer in San Francisco.
This is her blog.

While we intuitively expect such behaviors on the part of users, I have, in fact, observed them time and time again in usability testing. However, these user behaviors lead to some implications for user assistance design that might seem counterintuitive, as follows:

• Do not introduce required conceptual information before a user engages in activities that require those concepts.
• Do not explain business rules or constraints before the user encounters their constraining effects.

The key word in both statements above is before. Although both implications seem to fly in the face of good instructional design, they accommodate the reality of user behavior within an interactive medium.