The importance of creativity is being increasingly recognized by economists; however, the possibility that emotional factors determine creative processes is largely ignored. Building on 1,400 letters written by three famous music composers, I obtain well-being indices that span their lifetimes. The validity of this methodology is shown by linking the indices with biographical information and through estimation of the determinants of well-being. I then exploit the data and provide quantitative evidence on the existence of a causal impact of negative emotions on outstanding creativity, an association hypothesized across several disciplines since the antiquity that has not yet been convincingly established.