Padmanabhanunni, A., and T. B. Pretorius. “When Coping Resources Fail: The Health-Sustaining and Moderating Role of Fortitude in the Relationship Between COVID-19-Related Worries and Psychological Distress”. Social and Health Sciences, vol. 18, no. 2, 2020, pp. 28–47, https://unisapressjournals.co.za/index.php/SaHS/article/view/13171.