My advice is to just never give up. If you have researched to know that this is a good product that people would buy or even if it's not a consumer product. If it's a business you know that people are going to use or a service that people need, just don't give up. You never know. It might be the tenth time you get knocked down that you get back up again and turn that corner and take off. You can't let yourself stay down. You have to get back up and keep pushing forward with it.