My first 3-4 side projects were abject, miserable failures. It took me 5+ years of waking up to failures before I had something going that really gained traction. If I had just stuck with my first project, I am sure I would have gotten nowhere. So, have the guts to pull the plug on the project if you think it's the end of the road. It's okay - take a break, and you will bounce back even stronger.