I think this is a great post, and this is so true. The only caveat I would add is that sometimes ideas that don't seem ambitious end up being super ambitious. Facebook is a great example of that. In a video you can now find on Youtube, Mark Zuckerberg was describing theFacebook as a directory for college students. Not super ambitious. But then, he realized that he could open it up...and make it a platform, and that became super ambitious. You could say the same about Twitter, I think.

The risk of being too ambitious at first is being unable to ship your MVP because it appears too narrow vs. the ambition you have in your head. I know many entrepreneurs that failed because of that. Great entrepreneurs can ship a great MVP for an ambitious idea and thrive from there...