Can hard work be a natural talent?

One of the ideas I found in Wooden on Leadership is common among coaches. It could be paraphrased something like this.

You can't do anything about it if they are taller than you, but it's your fault if they work harder.

The implication is that genetics handed me my height (or body type or inherent speed or whatever), but I can choose how hard I work, my determination, my character. Does this really make sense, though?

We all know the value of hard work. Put in more effort, and (generally) we get more rewards. We all want more rewards, and we would all (for the most part) prefer the longer-term rewards that result from hard work than the short-term rewards of sloth. Why is there such a disparity in how hard we actually work, then?

Some people appear to have a greater work ethic than others. They seem to more easily put off pleasure now for rewards later, and seem hard to distract from the task at hand. Others (I find myself in this latter category most of the time) hardly think past the next meal, let alone the resultant heart attack from a fast-food diet 30 years from now. Given the choice between hard work or blowing it off until tomorrow, such folks (we) take procrastination.

Is there perhaps a natural limit to our work ethic, then? Resulting from nature or nurture, am I limited in how hard I can work, just as I am limited in how fast I can run and how tall I will grow? Can such limits be extended to other elements of character? Self-discipline, kindness, generosity, contentment?

I do not have an answer to this question. More importantly, perhaps, I do not know what I would do with an answer. Would this give me an excuse to slack off, knowing that I have reached my natural limit? Or inspire me to work harder to reach that limit and perhaps prove it a little bit wrong? Do you think our character has limits? What would that imply for you?