Philip Brickman, a social psychologist at the Northwestern University in the U.S., conducted an experiment. It was to observe the changes of emotions over time among those whose happiness greatly increased through an unexpected fortune and of those who drastically became unhappy due to paralysis caused by a sudden accident.
As time passed by, their level of happiness was reexamined; those who had felt high levels of happiness, owing to their sudden claim of fortune, no longer felt much happiness. Those who felt low levels of happiness due to an accident no longer felt unhappy.
The human brain has a habit of returning to its familiar previous state of emotion as time goes by even if it goes through emotional changes brought on by certain stimulation. A brain that is accustomed to negative emotions puts more meaning on negative occurrences throughout the day, and remembers them longer. On the contrary, a brain that is accustomed to happiness receives pleasant things more than unpleasant things. Even when it looks back on the day, it recalls happy things first.
Repetition is the only way to obtain the habit of feeling joy and thankfulness, throwing away negative emotional habits. That is why God asks us to:
“Be joyful always; pray continually; give thanks in all circumstances, for this is God’s will for you in Christ Jesus.” 1 Th 5:16–18