Dr Rangan Chatterjee argues that resentment, not external events, drives most stress. Holding onto past grievances keeps your stress response locked on even after the event ends. The happiest people are those who can let go.
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When we think about stress and the stress response, we are conditioned to think about external stresses. But holding on to resentment is an internal stressor. So, you are still activating your stress response by feeling it could have been different. They should not have done that. That person has wronged me. When you change your relationship with that past event, which has happened, It's no longer happening, right? It happened in the past. But by keeping it active within you, it is causing you internal stress by you not being able to let go. I passionately believe that the happiest people are those who can move on and let go.