Complex sentence: Though Twain earned a great deal of money from his writings and lectures, he invested money in ventures that caused him to lose a great deal of his earnings, most famously the Paige Compositor, which failed to turn a profit because of its complexity and imprecision.
Split into simpler sentences: Though Twain earned a great deal of money from his writings and lectures, he invested money in ventures that caused him to lose immense amounts of money. One particularly notable failed investment of Twain's was Paige Compositor, which failed to turn a profit because of its complexity and imprecision.