the.com/inadequacy

means The state of falling short of what's needed or expected — a lack of sufficiency, especially felt as a flaw in oneself.

from From Latin inadaequatus — 'in-' (not) plus 'adaequatus,' past participle of adaequare, 'to make equal,' itself built from ad- (to) and aequus (equal, level — the root that also gives us 'equal' and 'equity'). So at its core the word is purely mathematical: a thing not made equal to the measure it's held against. English borrowed it in that dry, technical sense before the feeling crept in — the word spent centuries describing insufficient supplies or evidence before it started describing people, at which point 'not equal to the task' quietly became 'not equal to oneself.'