参考文献:
[The Impact of Stress on the Immune System](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3967232/)
[The Role of Social Isolation in the Development of Chronic Disease](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4820515/)
[The Benefits of Optimism for Health and Well-being](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4145333/)