[...] sitting still and concentrating on just one task for an extended length of time is, as a pratical matter, impossible. If you said, 'I spent the whole night in the library, working on some client's sociology paper,' you really meant that you'd spent between two and three hours working on it and the rest of the time fidgeting and sharpening and organizing pencils and doing skin-checks in the men's room mirror and wandering around the stacks opening volumes at random and reading about, say, Durkheim's theories of suicide.