Whenever I meet someone who I admire, I do something I am decidedly good at: I overanalyze like crazy! So over the past few years as I've known this colleague, I have hypothesized that her success, while partially dependent on her intelligence and energy, is largely owed to a perspective that sees beyond obstacles to the desired result.
Here goes more analysis: she is completely unafraid. She's been going for what she wants for so long that she expects success and has dealt with failure enough times to feel able to cope with it. She doesn't allow excuses or "what ifs" to keep her from what she wants. I am constantly finding reasons why something isn't feasible, from feelings of inadequacy to concerns about being overscheduled, or a sheer lack of drive.
There are certainly cases where what we want is out of reach. But in my current situation, opportunities abound. Why not take what I want?