You should know that the 'Marshmallow Test' is a poor study. The general conclusions after follow up were that children had an intrinsic self-control mechanism that influenced success rates in later life. However, the original experiment failed to control for several factors, least of which was socio-economic status. Subsequent controlled replications show that these factors have a significant influence on the outcome, suggesting that resisting temptation is less about self-control/will power and more about food security. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6050075/