People have a baseline level of subjective happiness that they pretty much stay around no matter what actually happens in their life.
This is probably not completely true, depends what you mean by happiness.1 My intuition is to be pretty skeptical of the idea: it feels like something rich people say so they don't have to feel bad about their lives being better than others'.
Maike Luhmann et al., “Subjective Well-Being and Adaptation to Life Events: A Meta-Analysis on Differences Between Cognitive and Affective Well-Being,” Journal of Personality and Social Psychology 102, no. 3 (March 2012): 592–615, https://doi.org/10.1037/a0025948.