Don’t fall into the trap on working on the design for too long, the odds are that your designer and manufacturer would like to finish your project as quick as possible to collect their money so the option of dragging your feet will affect you and other people. Your designer will inform you that you have a limited period in which you can modify your design so be sure you know the exact direction you want to follow with the design.
People tend to make more time thinking during the concept / idea phase of the product. Is the idea really that feasibly and will people really want to buy it? The question I hear all the time. The more you look at your design the more you are going to fall in love with the idea. This is little bias as most of the time you are going to like the design as why would you continue with it. Ask friends and family if you are on the right track or if you need to modify the design.
Not all of us do have money to pursue a new product. If you are one of those try and get interest from friends or family or even investors to help push you along. Don’t try and start the design and employ people when you can’t pay them for the service this will just create a bad working relationship and further wasted time.