Research shows that half of the predicted difference in career success (i.e., promotion, compensation, industry recognition) is due to this one variable.
Model derived from Ronald Burt's research (above link).
Simply put, according to multiple, peer-reviewed studies, being in an open network instead of a closed one is the best predictor of career success.
But it is not all sunshine and rainbows. It is challenging, because it requires assimilating different and conflicting perspectives into one worldview, which is a considerable cognitive payload. Managing your time to connect with a broad network is also difficult. It requires sacrifice of things that are more fun and easier. It requires a belief that "turning up" is very important, even when not obvious. It requires you to engineer serendipity in order to unearth opportunities. And large and disparate networks can be a force multiplier.