Sunk Costs Fallacy is a logical fallacy in which someone argues that something has to continue (project, business etc.) despite being fruitless and unpromising only because a lot of resources has already been used to maintain the project.
Stan: I have spent so much time, resources and money on my project, I just can't give it up.. Even though it's not working out now, I have to try more and the adoption rate will rebound. All these efforts don't have to be in vain.
Mary: I understand that you feel bitter and you don't want to give up your project. But the fact that you have spent much on the project doesn't have to define what you're going to do next. You clearly didn't find a product-market fit, even though you have a nice product. It's time to move on, scrap the project and start something new benefiting from the experience from your previous project.
Full dialogue here: All argumentation fallacies