Here's how I interpret that explanation. Overisolation hobbles your decisioning skills by depriving you of both data and context (the information and the contextualization generated through social interactions). Overconnectedness hobbles you by skewing both your data and your context to whatever the popular preoccupations of your social circle happen to be at this time. If you fall into either "outlier" category, you become less influential in your social network. That's because your insights have become less valid, hence less useful, to the groups that might otherwise pay attention to you.
Influence is all about holding people's attentions through the expectation that you're worth following. In other words, you're slightly "strange" (that is, unique) without becoming too "estranged" (aka irrelevant).
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