Book excerpt: Fortune magazine editor Geoff Colvin offers new evidence that top performers in any field are not determined by their inborn talents. Greatness, he argues, does not come from DNA but from practice and perseverance honed over decades. The key to this is how successful people practice, how the results of practice are analysed and how they learn from their mistakes. This new mindset will change the way reader's think about their jobs and careers, and will inspire them to achieve more in all they do.