In order to”dent the universe” (with deference to Steve Jobs), you have to think big. If you think big, its is highly possible you will fail…big. You’ll work just as hard making a small idea successful so you might as well go for the dent.
The other side of this is that entrepreneurship is not a part-time job. You have to be all in, what ever you do or you’ll be in the no man’s land between success and failure.
Dharmesh Shah writes a very fine blog: OnStartups at http://onstartups.com/