The Brobdingnagian king knows shockingly little about the abstractions of political science, yet his country seems prosperous and well governed. Similarly, the Houyhnhnms know little about arcane subjects like astronomy, though they know how long a month is by observing the moon, since that knowledge has a practical effect on their well-being. Aspiring to higher fields of knowledge would be meaningless to them and would interfere with their happiness. In such contexts, it appears that living a happy and well-ordered life seems to be the very thing for which Swift thinks knowledge is useful.
Swift also emphasizes the importance of self-understanding. Gulliver is initially remarkably lacking in self-reflection and self-awareness. He makes no mention of his emotions, passions, dreams, or aspirations, and he shows no interest in describing his own psychology to us. Accordingly, he may strike us as frustratingly hollow or empty, though it is likely that his personal emptiness is part of the overall meaning of the novel. By the end, he has come close to a kind of twisted self-knowledge in his deranged belief that he is a Yahoo. His revulsion with the human condition, shown in his shabby treatment of the generous Don Pedro, extends to himself as well, so that he ends the novel in a thinly disguised state of self-hatred. Swift may thus be saying that self-knowledge has its necessary limits just as theoretical knowledge does, and that if we look too closely at ourselves we might not be able to carry on living happily.