Found via Tim Ferriss.
During the nine months of 1951 that saw him working on his novel, East of Eden, author John Steinbeck began each day of writing by penning, in his notebook, a brief letter to his editor and good friend, Pascal "Pat" Covici. Early-1952, with the book finished, Steinbeck wrote him a final letter — a dedication to Covici in which he spoke of the frustrations and insecurities faced by an author during such a process. It can be read below.
