Stock returns are a key factor in explaining risk, and investors look for companies with favorable trading performance. In selecting these companies, several factors affect their returns. This mixed-method research was conducted with the aim of presenting a model to examine the impact of hormonal (cortisol and testosterone) and hereditary factors on financial market stability and investors' trading performance, taking into account the role of COVID-19, during the period 2017 to 2019. A regression model was designed to examine the relationships between the aforementioned factors and the control variables. The results showed that the hormones cortisol and testosterone did not have a significant effect on trading performance, while heredity has a significant positive effect, COVID-19 increases the effect of cortisol on trading performance and reduces the effect of heredity. Also, cortisol has a significant negative effect on financial market stability, while testosterone and heredity have no effect. COVID-19 increases the intensity of the influence of cortisol and heredity on financial market stability. Hormonal changes alone do not affect trading performance. Finally, a significant difference was observed in investors' trading performance during and before COVID-19. Investors should consider natural and unnatural factors, their hormonal and hereditary characteristics, and societal conditions in their decision-making.