Do ambitious people tend to succeed?

Or do they eventually succumb to the reality of life and make peace with settling for less than what they originally sought? There seem to be a lot of respected people in this world that got where they are at least partly because of ambition, and also a lot of people that never realize their goals. What is the difference between those that make it and those that don’t? Hard work and inspiration as Edison suggested? If luck is a factor and you don’t have it, at what point do you ‘cash in your chips’ and settle?