"I was a terrible student, always staring out windows or looking at the clock, waiting for the class to be over," astronaut Scott Kelley recalls in his new book, Endurance. "I managed to graduate from high school, in the bottom half of my class." He enrolled in the only college that accepted him.

Kelly's disappointing academic experience failed to predict the success he would find 250 miles above the earth's surface, whizzing around the planet at 17,500 miles per hour. Kelly would go on to complete four flights aboard the International Space Station and spend a record-breaking year in space.

Kelly's path wasn't easy. He had to overcome cynics and doubters who didn't just think he'd never succeed; they told him so.

One day Kelly walked into a campus bookstore and a title captured his attention. It was The Right Stuff by Tom Wolf. Kelly was drawn to the adventures of Navy test pilots who undertook the immensely risky launches as the first Americans in space. Kelly said he closed the book and become a different person.

He decided to be a Navy pilot. There was just one hurdle. Kelly had ADHD, undiagnosed and misunderstood at the time he was attending school. "The path to becoming a naval aviator is an extremely competitive one, and I was still a chronic under performer with a terrible academic record," Kelly wrote. 

Kelly couldn't get into a military academy, so he chose to apply to the Merchant Marine. He spoke to the dean of admissions. It's an experience Kelly won't forget. "I want to become a commissioned officer in the Navy. My goal is to fly fighter planes and land on aircraft careers," Kelly boldly told the admissions officer. In Kelly's mind the goal was "clear and compelling." The man looked at Kelly, closed the folder on his desk that contained Kelly's transcripts and said:

"I'm sorry, son. There's just nothing here to indicate that you would be successful. Your high school grades are pretty terrible. Your SAT scores are below the average for our incoming freshmen. Your grades in your first semester of college are no better than high school...you wouldn't succeed here."

Stunned and close to tears, Kelly made a commitment to challenge himself at every level. He returned to college and took even more demanding courses. It was "a mighty struggle," but Kelly eventually performed well enough to transfer to a small Maritime school, became a Navy test pilot and was accepted into the ultra-selective NASA astronaut training program.

Reading The Right Stuff was the pivotal moment in Kelly's life. It gave him a vision of what he could be. But it was his vision, his goal. Nobody else shares your vision for your life or understands your calling, which is why it's easy for other people to talk you out of it.

Cognitive neuroscientists say it's very important to cultivate an optimistic attitude to counter the skepticism you'll inevitably face when sharing your dreams with people.  "In order to progress, we need to be able to imagine alternative realities--not just any old realities, but better ones, and we need to believe them to be possible," writes Tali Sharot in The Optimism Bias. Sharot says that when people believe a goal is not only attainable, but very likely to be attained, it leads people "to act vigorously," making it more likely that "the desired outcome will be realized."  

Don't let the bozos get you down.

Steve Jobs had a big, bold vision to make computers accessible to everyday people. He also realized how easy it is for most people to be talked out of pursuing their goal. One of the most quoted lines from Jobs' Stanford Commencement Address is: "Your time is limited, so don't waste it living someone else's life. Don't let the noise of other people's opinions drown out your own inner voice. Have the courage to follow your heart and intuition."

Jobs knew that innovation and success requires courage; courage in the face of "the bozos," as he liked to call them--the people who will drag you down and squash your dreams.

Kelly's story is for anyone with a dream. Kelly says the message he's conveying is that you can do more than you think you are capable of doing. Your lack of experience, a challenging background, or a mediocre school record doesn't have to be a limitation...unless you agree to it.