around the real life mean, it should be locally kinda linear
Even in personality and mental health, the PGSs rarely-if-ever account for literally zero percent of the variance. Normally the linear term of a Taylor series is not zero.
I think what you’re missing is: the linear approximation only works well (accounts for much of the variance) to the extent that the variation is small. But human behavioral differences—i.e. the kinds of things measured by personality tests and DSM checklists—are not small. There are people with 10× more friends than me, talk to them 10× as often as me, play 10× more sports than me, read 10× less than me, etc.
Why? As in my other comment, small differences in what feels rewarding and motivating to a person can cascade into massive differences in behavior. If someone finds it mildly unpleasant to be around other people, then that’s a durable personality trait, and it impacts a million decisions that they’ll make every day, all in the same direction, and thus it impacts how they spend pretty much all of their waking time, including even what they choose to think about each moment, for their entire life. So much flows from that.
Even in personality and mental health, the PGSs rarely-if-ever account for literally zero percent of the variance. Normally the linear term of a Taylor series is not zero.
I think what you’re missing is: the linear approximation only works well (accounts for much of the variance) to the extent that the variation is small. But human behavioral differences—i.e. the kinds of things measured by personality tests and DSM checklists—are not small. There are people with 10× more friends than me, talk to them 10× as often as me, play 10× more sports than me, read 10× less than me, etc.
Why? As in my other comment, small differences in what feels rewarding and motivating to a person can cascade into massive differences in behavior. If someone finds it mildly unpleasant to be around other people, then that’s a durable personality trait, and it impacts a million decisions that they’ll make every day, all in the same direction, and thus it impacts how they spend pretty much all of their waking time, including even what they choose to think about each moment, for their entire life. So much flows from that.