A Block Distraction Project, or BDP as Kevin calls it, is his way of dealing with what some writers refer to as Writer's Block.
This can be a devastating event for some writers, while others don't believe it even exists.
It could be the way he writes or the fact that he serially-publishes most of it, but from time to time he finds that his characters stray from their plotted path and cause him to write himself into a corner.
When this happens, he simply switches to another project for a while. Then revisits it later to see if a solution comes to him. He has the uncanny ability to compartmentalize projects and often has three or more on the go and many more just in the idea stage, yet he manages to switch projects like they're socks and doesn't get confused as to where he and his characters are in the story.