History is filled with stories about small opportunities that are the start of "something big" but the reality is that an opportunity is just that. Small opportunities presented to a person with vision and the power or desire to carry out that vision can indeed lead to big things.
An old addage purports that "chance favors only the prepared mind." In the case of opportunity, that may be very true. From the outside, it may seem like a person, presented with a small opportunity, magically transforms it into something larger than life.
In all likelihood, that person has prepared himself (or herself) for the possibility of something big and simply recognizes an opportunity for what it is. By having prepared oneself, by having a vision of the end result; by acquiring skills needed to carry out the vision; by understanding the challenges that one might confront and by contemplating potential solutions; by recognizing and understanding the need for additional assistance to carry out one's vision; one prepares for success.
A critical component of success is simply recognizing an opportunity when it is presented. Having a clear understanding of one's vision is the single most important facet of recognizing opportunity. Sometimes vision comes in a flash of inspiration, but more often, it is the product of serious study and thought.
Finally, the willingness to try to achieve one's vision is critical to success. Having an open mind, in addition to a prepared mind, can indeed transform a small opportunity into a great enterprise.