Raymond E. Feast started writing just to "see if he could do it," J. K. Rowling came up with the idea for Harry Potter while stuck on a delayed train between Manchester and London, and Steven King's famous "Carry" was an idea he crumpled up and threw away -- Steven only decided to finish the story because his wife found the discarded story and persuaded him to write it.
Moral of these stories? Whatever is you think "might be fun" or "might be a good idea" is an excellent idea. It's a million-dollar idea. The only difference between your idea and a successful idea is perseverance. Take your biggest inspiration and turn it into your biggest success.
If you're not feeling confident, eat more fresh fruits and vegetables. Raising the alkalinity of your blood will naturally boost your confidence.