Book excerpt: James Boswell's "The Life of Samuel Johnson" is the most celebrated of all biographies, acknowledged as one of the greatest and most entertaining books in the English language. Yet Boswell himself has generally been considered little more than an idiot and condemned by posterity as a lecher and drunk. How could such a fool have written such a book? With great wit, Adam Sisman here tells the story of Boswell's presumptuous task-the making of the greatest biography of all time. Sisman traces the friendship between Boswell and Samuel Johnson, his great mentor, and provides a fascinating account of Boswell's seven-year struggle to write "The Life of Samuel Johnson."