Working: Researching, Interviewing, Writing by Robert A. Caro:
That was the thing that made me doubt the most. When I had started, I had firmly believed that I would be done in a year, a naïve but perhaps not unnatural belief for someone whose longest previous deadline had been measured in weeks. As year followed year, and I was still not nearly done, I became convinced that I had gone terribly astray.
This feeling was fed by the people Ina and I did know. I was still in the first year of research when friends and acquaintances began to ask if I was “still doing that book.” Later I would be asked, “How long have you been working on it now?” When I said three years, or four, or five, they would quickly disguise their look of incredulity, but not quickly enough to keep me from seeing it. I came to dread that question.