What does the 'hedonic treadmill' refer to?

The concept of the 'hedonic treadmill' describes the phenomenon where individuals tend to return to a relatively stable level of happiness despite significant positive or negative events or changes in their lives. This implies that although people may experience temporary boosts in happiness due to achievements, wealth, or other sources of pleasure, these feelings often don't last, and a person will eventually revert to their baseline level of happiness.

In contrast to the other options, which focus on aspects either related to growth in happiness or measurement of life satisfaction, the correct answer highlights the inherent balance that most individuals seem to exhibit regarding their emotional states over time. This is critical in understanding human behavior and the challenges people face in pursuing lasting happiness through external accomplishments.