Here’s a 2018 article from two researchers involved in the Dunedin (New Zealand) Longitudinal Study. They coauthored many studies, including People had the same personalities at age 26 that they had at age 3.
The paper’s grand hypothesis was:
“A single dimension is able to measure a person’s liability to mental disorder, comorbidity among disorders, persistence of disorders over time, and severity of symptoms.”
The coauthors partially based this on:
“Repeated diagnostic interviews carried out over 25 years, when the research participants were 11, 13, 15, 18, 21, 26, 32, and 38 years old, and include information about seven diagnostic groups: anxiety, depression, attention deficit hyperactivity disorder, conduct disorder, substance dependence, bipolar disorder, and schizophrenia.”
https://ajp.psychiatryonline.org/doi/full/10.1176/appi.ajp.2018.17121383 “All for One and One for All: Mental Disorders in One Dimension” (not freely available)
More about the coauthors:
“Dunedin and other studies show that most people have at least one episode of mental illness during their lifetime.”
What compels people to search for “universal truths” instead of personal truths? Are we afraid of our feelings?
What if the grand hypothesis worth proving was: For one’s life to have meaning, each individual has to regain their feelings?