To many, the Great Work seemed a Great Folly. His persistence, his desire to verify even the smallest detail, were ridiculed in the press. It seemed as if he would never finish; he almost abandoned the book in despair. He sank into glooms which rendered him incapable of work for weeks on end. Meanwhile, lack of money caused him constant anxiety. He kept abandoning his book to pursue his career, often for months at a time. At various points he lapsed into heavy drinking, which left him hung over and unable to write. Often he worked while eating, concentrating despite the domestic distractions around him. He neglected his wife, who was terminally ill with tuberculosis; when she died he was tormented by remorse. As he accumulated more and more source-material, the book swelled; he was warned that nobody would buy such a huge biography at the high price that it would inevitably command. In the wreckage of his disordered mind, he clung to the memory of Johnson as a shipwrecked sailor clings to a rock. In the midst of his disappointment and despair, Boswell immortalized the life of the man he revered above all others.
---from Boswell's Presumptuous Task by Adam Sisman