Nugacity

For the first time in his life of twenty-five years, Leigh Newcomber was seriously thinking of personal and practical matters; and this mental state being an untrained one, he jumped from impulse to impulse, and from reason to nugacity; and after a while reason and impulse became so commingled as to leave him in a bewildering maze of mental and moral incertitude.

In the poem "Among School Children" Yeats gives the nugacity of temporal life a bittersweet rendering.