The link of maths and happiness is not straightforward. Individual accounts of a happy (euphoric) or unhappy (dismal) life are mostly referred to psychologists for treatment. The biografies (documentaries) or fictional biografies told in novels or cinema allow to trace the changing moods of the personalities over time. This resembles life course research. In happiness research social scientist ask questions like “Overall, how satisfied are you with your life“. Measured over time or coded from biografies this allows to reconstruct happiness trajectories. At this point the maths of happiness enter the stage. Long periods of observations yield interesting patterns of curved lines, rarely simple linear trajectories. Social scientist speak of within person variability in contrast to between persons variability. After all, the (short-term superior) happiness of your neighbor might simply be due to the fact that they are doing drugs.
Whatever, try to remember a bit of your high school maths and the bore to deal with “curve discussions or sketching” beyond the manifold shapes of your classmates. Lots of interesting information derives from growth or decline rates, tangent lines, stationary or inflection points. Different starting points or so-called intercepts vary between individuals as well as he potential to cross the Zero-line on one of the axes. Additionally, in geometry you would compare syncronicity of curved lines as well as forms of symmetry for the curve(s). This will simplify or comlexify your perspective on the happiness trajectories of people or characters in a novel.
We are so used to narratives or videoss with a happy end, yet we appreciate the complex trajectories and (multiple) troughs main characters have to pass. Novels teach us about tricky inflection points and subsequent trajectories as well. The maths of happiness, however, is rather simple in comparison.
(Image from Toronto District Christian High School -pdf p.207). 
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