Reading Usable Help
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Gordon R. Meyer
Too simple to believe
Macworld writes When Installing Software is Too Simple about the process of installing applications on Mac OS X, which involves dragging the application icon to your Applications folder, and how this one-step, no-installer process befuddles some Windows users. It's all about the expectations that users bring to the table and if things are too foreign, regardless of how simple they might be, they disbelieve the instructions they're given. A good example of needing to know your audience.
Part of the difficulty in the examples the article uses is that the installation instructions consisted of an illustration only. No words at all, which is a very challenging instructional task. After you read the article, check out the 2003 Usable Help Special Report Using Background Images in Mac OS X for technical details about the general technique.