In fact, the better the documentation, the simpler it is to use a program. Take the Apache web server for example, it comes with heavy documentation. This article tries to encourage programmers to document their projects, as well as to provide ideas and tips on doing so. More documentation means easier usage. More documentation means better add-on modules.
More documentation means happier users.
As soon as a user gets stuck trying to get a program feature to work, he or she starts to read that program's documentation. Source code, of course, because somebody may want to add features to the program. Examples of usage to supply a working basic configuration file and document it heavily. This list can be extended further. But in general a well-documented program will cover at least these, and it will do so in a readable fashion.