Few ideas in business conjure more vivid images of bold individualism than the do-it-yourself entrepreneur. Entrepreneurs go it alone, the mythology insists. The image is irresistibly romantic and deeply entrenched. It is also completely misleading.There is groundbreaking evidence that the most vibrant entrepreneurship is developed by high-impact entrepreneurs when they operate in tight-knit networks, nurturing fellow risk-takers and trading know-how, capital and tough love. We’ve mapped this cross-pollination across generations and continents. And we’ve done this not by looking at the most obvious communities, like Silicon Valley, but at some of the harshest terrain for innovation.