1. Lack of follow through
It doesn't matter how good your idea is, it doesn't matter how excited you are about your website if you never follow through and create one it's not going to help you one bit.
2. Waiting until things are perfect to launch (Procrastinating)
Don't fall into this trap. It's easy to think I'll launch my site when I get things just right, when they look perfect. It's better to launch something than nothing. Once your website is out there you'll be committed to the process. If it's horrible you'll be all the more motivated to make it better. You'll also be in a place where you can gather honest feedback and make the appropriate tweaks.
3. Not being able to edit your website
It's a major hindereance when you can't make changes to your website yourself. Relying a programmer will only put you at the mercy of someone else. That's why you need a platform like WebStarts where you can build your website and make those little tweaks and changes on your own. Keeping your webiste updated and reacting to feedback from visitors is paramount to your websites success and nobody you hire to work on your website is going to care as much as you, or understand your business the way you do.