David and Goliath: Underdogs, Misfits, and the Art of Battling Giants

and Adam Grant argue, in a brilliant
paper, that, in fact, nearly everything of
consequence follows the inverted U:
“Across many domains of psychology,
one finds that X increases Y to a point,
and then it decreases Y....There is no
such thing as an unmitigated good. All
positive traits, states, and experiences
have costs that at high levels may begin
to outweigh their benefits.”
3 My father, a mathematician and
stickler on these matters, begs to differ. I
am oversimplifying things, he points out.
Inverted-U curves actually have four
parts. Stage one, where the curve is
linear. Stage two, where “the initial
linear relation has flagged.” This is the
area of diminishing marginal returns.