Sacks discovers thoughts by writing

It seems to me that I discover my thoughts through the act of writing, in the act of writing. Occasionally a piece comes out perfectly, but more often my writings need extensive pruning and editing, because I may express the same thought in many different ways. I can get waylaid by tangential thoughts and associations in mid-sentence, and this leads to parentheses, subordinate clauses, sentences of paragraphic length. I never use one adjective if six seem to me better . . . .  All this creates problems of organization. I get intoxicated, sometimes, by the rush of thoughts and am too impatient to put them in the rights order. But one needs a cool head, intervals of sobriety, as much as one needs that creature exuberance.

Oliver Sacks, On the Move: A Life (New York: Alfred A. Knopf, 2015)