Marchant, D. C., Polman, R. C. J., Clough, P. J., Jackson, J. G., Levy, A. R., & Nicholls, A. R. (2009). Mental toughness: managerial and age differences. JOURNAL OF MANAGERIAL PSYCHOLOGY, 24(5), 428-437. https://doi.org/10.1108/02683940910959753