Here's a (verified true) story about George Dantzig, the mathematician whose significant contributions to Operations Research and systems engineering have made him famous.
One morning in 1939, as a college student at Berkeley, George arrived late for Prof. Jerry Neyman's statistics class. He quickly copied the two problems on the board, assuming they were the homework assignment. It took him several days to work through the two problems, but finally he had a breakthrough and dropped the homework on Neyman's desk the next day.
Six weeks later, on a Sunday morning, George was visited by his excited professor, announcing the acceptance of a paper based on his proof! Since George was late for class, he had not heard the professor announce that the two unsolved equations on ! the board were mathematical mind-teasers that experts had not yet cracked.
But George Dantzig, working without any thoughts of limitation, had solved not one, but two problems that had stumped mathematicians for years.
Simply put, George solved the problems because he didn't know he couldn't. You are not limited to the life you now live. It has been accepted by you as the best you can do at this moment. Any time you're ready to go beyond the limitations currently in your life, you're capable of doing that by choosing different thoughts. All you must do is figure out how you can do it, not whether or not you can. And once you have made your mind up to do it, it's amazing how your mind begins to figure out how.
A person is limited only by the thoughts that s/he chooses.
(Thanks to Sebin Thomas for sharing this.)
When we do not know that something is difficult (or impossible) that mindset itself somehow makes us approach it in a more effective manner. It is why Richard Bach's little 1970 storybook, Jonathan Livingston Seagull, still sells and inspires millions. Unfortunately our increased knowledge of any subject often makes us more aware of what is not possible. The challenge is to imbibe a positive belief that goes against the known facts. Successful salespeople and ambitious sportspersons know the trick.