The cost has always sunk. The fallacy is assigning it value. In the broadest sense the fallacy is about not wanting to waste past effort. Whereas in reality 'w

The cost has always sunk. The fallacy is assigning it value. In the broadest sense the fallacy is about not wanting to waste past effort. Whereas in reality 'wasting' past effort doesn't cost anything but wasting future effort does. Now it can be hard to tell to what extent your past effort actually brought your goal closer, so it can be hard to judge if continuing effort may or may not be worth it, but if you're arguing it is worth continuing because you don't want to waste past effort, and not because the goal is worth the remaining effort required, then the reasoning is fallacious.