"Positive and negative emotions cannot occupy the mind at the same time."

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You know, the standard state for people is 'mildly pleasant.' Negative emotions are quite rare, and extremely positive emotions are rare. But people are mildly pleased most of the time, they're mildly tired a lot of the time, and they wish they were somewhere else a substantial part of the time - but mostly they're mildly pleased.

— Daniel Kahneman