92 This necessary vigilance does not demand that young people be removed from the society in which they must live and save their souls; but that today more than ever they should be forewarned and forearmed as Christians against the seductions and the errors of the world, which, as Holy Writ admonishes us, is all "concupiscence of the flesh, concupiscence of the eyes and pride of life." Let them be what Tertullian wrote of the first Christians, and what Christians of all times ought to be, "sharers in the possession of the world, not of its error."
Source: Divini Illius Magistri (Vatican.va)