Reader's fatigue is a form of fatigue that happens when reading. It usually occurs when the reader is reading one or more long, poorly spaced paragraphs of writing.
Reader's fatigue is not often associated with professional writing. Most professionals are usually educated well enough in the art of writing to not put their audience through reader's fatigue. Thus, it is more frequently affiliated with amateur writing. It is quite common for reader's fatigue to come from reading amateur work that appears on the Internet, due to the fact that many people who write on the Internet (whether it be for a web site, a message board, or just for e-mail) are not professionally trained in writing.