Not able; not having sufficient strength, means, knowledge, skill, or the like; impotent' weak; helpless; incapable; -- now usually followed by an infinitive or an adverbial phrase; as, unable for work; unable to bear fatigue.
My mother said I must always be intolerant of ignorance but understanding of illiteracy. That some people, unable to go to school, were more educated and more intelligent than college professors. Maya Angelou
Men ought either to be indulged or utterly destroyed, for if you merely offend them they take vengeance, but if you injure them greatly they are unable to retaliate, so that the injury done to a man ought to be such that vengeance cannot be feared. Niccolo Machiavelli
People who are unable to motivate themselves must be content with mediocrity, no matter how impressive their other talents. Andrew Carnegie