[A2A] I am also a simple average guy and I have an even bigger handicap: "I am not that driven to achieve greatness as your question posits." So, I don't think I am qualified to answer this question. I am a simple, happy-go-lucky guy. I just take whatever comes along my way, if it interests me. There is only one thing that I worked really hard for in my life and when I achieved it, I decided it was not worth pursuing because it was way beyond my capacity (as I had to work really hard to get it). After that, I have been realistic about my capacity and choose my path accordingly.
For more insights on my understanding on this topic, please read the answer to a question I had previously answered: Can anyone achieve anything he wants (e.g. GATE examination)? Does aptitude matter or perseverance and attentiveness is key?
I wanted to be a Shane Warne (he was the best leg spinner in cricket), but even if I tried I could not become one. Believe me, I wanted to be famous like him. You might have seen some horrible singers on "Indian Idol" or "American Idol" or in your close circles. So, even if they practice for a lifetime, they cannot become good singers. I am one such person. I have taken tabla classes, harmonium classes, singing classes, but could not pick up anything in any of those classes, although I wanted to be good at music and singing. But, one of my friends who had no training could play very good drums just by listening to the songs.
So, every person is "gifted" with certain attributes. He can try to improve himself but there are limitations on how much he can improve. Just like there are limitations on human beings as a class, even if they tried, they could not fly. Even the best of the humans cannot fly. Similarly, there are individual limitations of each person beyond which they cannot improve themselves in a certain area, even if they tried very hard.
So, life is like a constraint optimization problem. There are certain constraints in everyone's life and one has to work around them. It is best to choose a profession or passion in which the upper limit for you is high, so that you can grow a lot. If you choose a path, where you are severely constrained, it will be frustrating.