Twain was often obsessed with his daily page-count. His pages had only 70-80 words. A newly discovered letter … reads in part: “You see, I write on an average, 400 pages of manuscript per working month — to do this, one must make it a rigid duty to refrain from writing family letters — there isn’t any other way. I can’t write one before work, for then I should go to work with depleted fuel; I can’t write one after work, for that would waste me like sickness…. [W]hen I do write one, I don’t do any work that day. [Emphasis added.]
Despite his supposed letter-writing abstinence, Twain wrote thousands of letters in his lifetime, many of them to family members.
According to Powers, he also weathered many bouts of writer’s block.
[Twain]’s manuscript … was nowhere near finished by January 1871…. “Tell you what I’ll do, if you say so,” he offered to Elisha Bliss in the first month of the new year. “Will write night & day & send you 200 pages of MS. every week … & finish it all up the 15th of April….”
He was kidding himself. He was in no shape to write night and day. His creative interest in the book had stalled, a recurring affliction that Mark Twain eventually came to understand metaphorically as his “tank” running dry. He also came to understand — later — how to deal with the “dry tank”: put the manuscript aside and wait, for months or years, until the tank filled up again. That insight was not available to him in early 1871; and so he tried, in effect, to will the manuscript to completion — scavenging previously published reminiscences of his time in the West, the notes [his brother] had sent him — anything that would add bulk….