That's a loaded question. To start with, it really depends on what your ambitions are. If they're something like "becoming the best [insert something] in the world," or "be the first person to...," etc., then you're essentially competing with everyone else who has that ambition, and the odds of you winning at the time when you first adopt the ambition are extremely low no matter who you are. But if they're something like "opening my own restaurant," or "becoming super talented at [insert something here]," etc., then it's really just up to your resolve. And obviously there are a bunch more types of ambitions, all with their own stipulations; the point is that the context is always relevant. And even if the only thing standing between you and your dreams is your own resolve you still have to ask yourself whether the dream is worth the amount of effort it will take you to accomplish, and that isn't a decision you make once and move on, it's something you'll constantly be grappling with until you reach your goals.
So, as usual, I guess my answer is "it depends."
What are some of your ambitions?