The collision between scientific thought, incapable of giving meaning to life, and religious morality lacking personal justification raises in Unamuno the urgent question of the meaning of existence. The irreconcilable antagonism between the heart and reason, between everything and nothing, leads Unamuno to the abyss of despair, where man must fight following the vitalist example of Don Quixote, whose faith is based on uncertainty. Pedro Cerezo-Galán in the introduction covers the vital and intellectual trajectory followed by Unamuno until he reaches his tragic conception of life and its embodiment in this now classic work.