As a 2nd year teacher, I've had my share of project lessons that have ultimately failed. Each one has a different reason for failing, whether instructions aren't clear enough, students don't understand, students don't listen, it just wasn't a good idea to begin with, etc. but nevertheless it is an idea that either needs some major overhaul or a trip to the garbage!
When you're in the middle of a project and you see it start falling apart, do you keep going and try to work through the issues/problems or do you scrap it all together and move on to something else? I have yet to figure out the right thing to do. My thought process leads me to want to believe that something can be learned from anything, even if it is learning what not to do. However, is it worth the headache of trying to hold something together when it is just determined to fall apart?