I agree completely. In the real world costs are often NOT completely sunk. I could even add to your list, e.g. employee morale. Along your lines of argument,

I agree completely. In the real world costs are often NOT completely sunk. I could even add to your list, e.g. employee morale. Along your lines of argument, you might say you've INVESTED money instead of just SUNK. At the same time, we also tend to hold on to obviously fruitless enterprises. So the real lesson of course is to try to be objective about what's really going on, suspending your ego for the benefit of the project. Which I'm sure we agree on!