What is the "Sunk Cost Fallacy" in freelance project management?

[Btaliat]

Most of the freelancers always fall victims of this fallacy. Majority of them do not want to walk away from tasks because they believe that they have spent so much time and money on the projects. However, it is better for freelancers to know how to walk away when the projects is taken time and as well the cost doesn't match up with the projects. What do you suggest a freelancer do when something like this happens?