The key to survival in a client-based profession like software development is recognizing the signals of a project heading south despite your best efforts. Here, difficult clients can be a clear impediment to your success.
In fact, anyone who has spent time working directly with clients has probably come across a few that reminded them of mythological beasts. Maybe the project kicked off well but took a wrong turn into a bureaucratic fog, only to die a slow death. Maybe a powerful executive suddenly rose up from behind the scenes to kill your project midway through. Maybe an unreasonable demand late in the game burned to a crisp your chances of ever getting paid.