What do you think of when you hear the word "genius"? Most of us, I suspect, picture a fellow in a white coat who squints into a microscope, twiddles a knob, and says, "Eureka! I've found the cure for cancer!" More often than not, though, scientific and creative discoveries are the result not of bolts of mental lightning but of long stretches of painfully hard slogging. This unromantic reality is the subject of "Sudden Genius?: The Gradual Path to Creative Breakthroughs," a new book in which the British biographer Andrew Robinson examines key moments in the lives of such giants as Marie Curie, Charles Darwin, Albert Einstein and Leonardo da Vinci. The conclusion that he draws from their experience is that creative genius is "the work of human grit, not the product of superhuman grace." Along the way, Mr. Robinson also takes time out to consider one of the most fashionable modern-day theories of genius—and finds it wanting.

The theory is known in England as "the 10-year rule" and in the U.S., where it has been popularized by Malcolm Gladwell, the author of "Outliers," as "the 10,000-hour rule." The premise is the same: To become successful at anything, you must spend 10 years working at it for 20 hours each week. Do so, however, and success is all but inevitable. You don't have to be a genius—in fact, there's no such thing.

K. Anders Ericsson, the psychologist who is widely credited with having formulated the 10,000-hour rule, says in "The Making of an Expert," a 2007 article summarizing his research, that "experts are always made, not born." He discounts the role played by innate talent, citing Wolfgang Amadeus Mozart as an example: "Nobody questions that Mozart's achievements were extraordinary. . . . What's often forgotten, however, is that his development was equally exceptional for his time. His musical tutelage started before he was four years old, and his father, also a skilled composer, was a famous music teacher and had written one of the first books on violin instruction. Like other world-class performers, Mozart was not born an expert—he became one."