Love this post by Jason Cohen on vetting a startup, in which he reveals the process he went through to vet two startup ideas in succession, and describing how the process turned out differently for the two ideas:
Let me dispose of any lingering ideas that WPEngine was a great flash of insight, born perfect from conception like a Greek God emerging from the ocean, a once-per-decade occurrence sourced from unsystematic inspiration. Let me also dispel your doubts that you can't produce similar ideas with similar results using a similar process. You can, because there's nothing magical in how I got to this point.
Like the mighty sudoku puzzle, there might actually be a process to this startup thing...
Inspiration and luck play important roles at the beginning, but turning a bright idea into a real business where strangers come to a website and part with money is an intentional process. A process you can learn and get better at.
Of course, some prefer the "luck" and "inspiration" theories.? It is convenient to think that you just need an idea. Read on in his blog for the details.