How much do we limit ourselves by our mindsets/attitudes and how much are we limited by things beyond our control? Does it vary? Why/how?

I doubt it.  Someone with an IQ of 100 is no match for a genius which is defined as someone with an IQ of 140 and above. HOWEVER potential alone means nothing. The smartest people in the world are of little value if all they do is sit and kvetch and moan and groan and complain and bit**. Anyone can do that. It doesn't take a genius. Here's where I digress.  Are you familiar with Thomas Gray's Elegy in a Country Churchyard? One line of it goes something like this..."full many a flower is born to blush unseen and waste its fragrance on the desert air".  What I wonder is how many unseen flowers have bloomed unseen whose fragrance we can never know?  All that wasted potential brilliance/fragrance? Lack of opportunities. No one there to support them or encourage then or show them the way or give them a break or nurture them or mentor them? We will never know the answer to that. It is just as well. We could not stand it. Thank you for your reply ISS! :)

IQ is a BS measure, actually. Google it--IQ isn't a good measure of intelligence at all. It's sort of like the SAT in that matter. Yes it measures certain metrics that very roughly judge someone's capabilities, but it doesn't test practical knowledge. It's a very bourgeois test as well. Just look it up. There is a LOT more to intelligence than just that. I have an IQ of 132 with subscores ranging fro 117 (Math) and 147 (Verbal). My math score isn't that high, but everyone knows me to be an extreme math nerd, and nobody knows me for my rhetorical skills. You can have a high IQ and not use it, and likewise you can have a lower IQ and use it. It's easier for someone of a high IQ to grasp a concept and think of new ones, but it doesn't mean someone of a lower IQ can't. Anyone can be a genius with enough effort and mentoring :) And this goes for everyone--high and low IQ. 

I may not be as smart as some other people I know--but I'm more dedicated and passionate than them--and in the end, dedication and passion is just as important as intelligence in how successful a person is at something :D

That's been repeatedly proven false. Genius ability is a born trait.