I didn't have a really good riposte to Clarissa, who the other day in a comment on my post about the threshold theory compared scholarship to rowing up a stream. The current is trying to bring you downstream, so if you don't constantly row, you will get further and further down. My perhaps too optimistic notion was that once you reach a certain threshold, with a solid scholarly base, you can always do scholarship. The base is cumulative, so the older you get the more you know, even if you forget some of what you know. Like the idea that "I've forgotten more about Spanish literature than you've ever even learned."
The field may change, but nobody really keeps up with every development anyway. If you are always reading, you will never be totally out of it. My father abandoned research in sociology and became a university administrator. He was dean of the college, and slightly older than I am now, when he caught a pneumonia that all but killed him. He was in what was essentially a medically induced coma for weeks, and was left almost entirely paralyzed. He had to learn to walk again, tie his shoes and button his shirt, and was disabled, with less than half the lung capacity of a normal adult, the rest of his life. He had to retire from administration, though he had a few year-long posts after he made a partial recovery. He also read up on some social theory, took some courses at UC Berkeley, and wrote a book calledThe New Public, published by Cambridge. Then he died at age 65, twelve years after his initial illness.
The paddling-up-the-creek metaphor is valid for people who never gain an initial foothold, who never quite overcome a weak base.I think I could write nothing for 10 years and still come back strong.
Burn-out is something else entirely. That's when there is an initial burst of energy, some promise, and then a career stalls in the middle. It happened to me, but I recovered fine.