Lyubomirsky refers to the “happiness set point” as an individual’s inherent, genetically influenced level of happiness. This set point tends to act as a baseline to which people return regardless of the various positive and negative experiences they encounter in life. In simpler terms, it means that external events, circumstances, or momentary ups and downs have only a temporary impact on our overall happiness.

Lyubomirsky defines “flow” as a state of deep engagement and complete absorption in an activity. When someone experiences flow, they become entirely immersed in whatever they are doing, to the extent that they lose their sense of time passing and even their self-awareness. It’s as if they are so deeply involved in the task that nothing else matters. Lyubomirsky emphasizes that these moments of flow can be particularly meaningful because they contribute significantly to feelings of happiness and fulfillment.

In the book, the concept of the “hedonic treadmill” signifies that people adapt to life changes, both positive and negative, and eventually revert to their baseline level of happiness. Lyubomirsky’s argument is that this phenomenon suggests that the pursuit of external factors, like accumulating wealth or material possessions, does not lead to sustained happiness. In other words, the initial boost in happiness that comes from these external changes is often short-lived.