Relative debilitation of yang is mainly caused by congenital deficiency, or postnatal malnutrition and endogenous impairment due to overstrain, or consumption of yang qi due to prolonged illness.
But through certain sensibilities Dorothea was as quick as he, and seeing her face change, he added, immediately, " But it is quite true that the best minds have been sometimes overstrained in working out their ideas" .