The Compulsion is what causes many bloggers to write about what happened to them or begin blogging in the first place. As the name suggests, it is a compulsion to write about their encounters with the Fears. It is unknown how many bloggers are actually under the Compulsion because of the difficulty in determining who is genuinely being affected by it. There are many different explanations for why The Compulsion occurs and what causes it.
In Hidden in the Trees, Joseph Steward revealed that he believed The Rake's whispers were the cause of the Compulsion, compelling people to spread information about the other Fears. This would cause humans to fight against them, serving as a distraction against them and allowing the Rake to accomplish its goals unopposed.
Tale of the Vikings reveals that, in Topography Genera, the compulsion to write about significant events in a Runner's life is referred to as "The Glass Prison" and occurs when a Fossil marks a Runner to die. Most Runners avoid "Prisoners," as anyone who writes about their events will surely only bring more danger with them. Why a Fossil would arbitrarily mark specific people to die and to write about their lives is currently unknown.