The academic cocoon
In the novel Enchantment, the main character, Ivan, gives a bitter assessment of his choice of an academic career, saying it was for "men who hadn't yet grown up."
The life he had chosen was a cocoon. Surrounded by a web of old manuscripts and scholarly papers, he would achieve tenure, publish frequently, teach a group of carefully selected graduate students, be treated like a celebrity by the handful of people who had the faintest idea who he was, and go to his grave deluded into thinking he had achieved greatness when in fact he stayed in school all his life. Where was the plunge into the unknown?
I don't believe the author meant to imply that an academic career is necessarily so insular. In the context of the quote, Ivan says his father, also a scholar, "hadn't stayed in the cocoon" but had taken great risks. But there is certainly the danger of living in a tiny world and believing that you're living in a much larger world. Others may face the same danger, though it seems particularly acute for academics.
It's interesting that Ivan criticizes scholars for avoiding the unknown. Scholars would say they're all about pursuing the unknown. But scholars pursue known unknowns, questions that can be precisely formulated within the narrow bounds of their discipline. The "plunge into the unknown" here refers to unknown unknowns, messier situations where not only are the outcomes unknown, even the risks themselves are unknown.