The regret for the loss of ancient illusions (the sole guarantee of happiness), caused by the advance of civilisation and knowledge, is a sentiment central to Leopardi.
Apart from in the Zibaldone, he expresses in very diverse writings, from his verses on Columbus in the Angelo Mai to the Discorso sugli Italiani (where we read of the “massacre of illusions”), through to the proemial Operetta Storia del genere umano/History of humanity:
Without illusions there can be no greatness of thought, nor poetry, “nor great deeds that are for the most follies” [14-23, 1082] “The most solid pleasure of this life is the vain pleasure of illusions” [51, 101-2, 125] illusions in ancient Greece [52, 3435-40] the real being nothingness, the only reality is illusions [99] “Nowadays superior minds have this property that they can so easily conceive illusions, and most easily and promptly loose them” [136-7] “Egoism devoid of illusions extinguishes the national spirit, virtue etc. and divides nations by heads” [160-1] they are extinguished by the advance of civilisation, and this provokes unhappiness [213-7, 232] a poem, albeit describing their vainness, provokes new illusions [259-61] “all pleasures are illusions or consist of illusion” [271-2] illusions are necessary to poetry [285-7] the effect of climate on illusions [349-51] Christianity is in part a surrogate of ancient illusions [423-33] the care of sepulchres is an illusion [471] “The presence and act of society extinguishes the illusions, whereas in ancient times it fomented and inspired them, and solitude foments them” [678-83] without, there can be no patriotism [923-5, 4135-6] the true philosopher loves illusions, because “The most capital of illusions” is to think that the world “can truly be something” [1715] it is illusions that bring truth [1849-60, 1961-2] “man would be happy if his youthful (and childhood) illusions were reality” [2684-5] “All is vain aside beautiful illusions and delectable frivolities” [3990].