20-year-old learns valuable lesson: Just having a big idea isn't enough

This is from a New York Times piece discussing venture capitalist Peter Thiel's Fellowship program. The program selects 20 entrepreneurs under the age of 20 each year to receive a $100,000 grant to pursue their ideas. One winner in particular has learned some lessons that took me many years to grasp:

John Burnham had bold plans to start a company to extract minerals from outer space. He quickly learned that $100,000 was not nearly enough to do that, so he came up with a new idea: creating models to make capital-intensive projects like space exploration economically viable. That idea also floundered, so now Mr. Burnham is figuring out what to do next. "It's been really eye-opening for me to realize that just because you have a big idea doesn't mean that's all it's going to take to make something happen," he said.