The hard part here is that you can't always decide what a failure is at the beginning.It's entirely possible that the market changes or your business changes, or a new product supercedes what you were doing. There are changes that make you re-evaluate later and you might decide to stop working on something.

It's a battle to dispassionately evlaute a project that's late and not working and ignore the costs. However, the costs spent are gone. You have to decide if future costs are better spent on this project or something else.