Most readers of The New York Times probably subscribe to what Paul Tough calls “the cognitive hypothesis”: the belief “that success today depends primarily on cognitive skills — the kind of intelligence that gets measured on I.Q. tests, including the abilities to recognize letters and words, to calculate, to detect patterns — and that the best way to develop these skills is to practice them as much as possible, beginning as early as possible.” In his new book, “How Children Succeed,” Tough sets out to replace this assumption with what might be called the character hypothesis: the notion that noncognitive skills, like persistence, self-control, curiosity, conscientiousness, grit and self-confidence, are more crucial than sheer brainpower to achieving success.