It is impossible for someone to dispel his fears about the most important matters if he doesn't know the nature of the universe but still gives some … - Epicurus

The happiness which belongs to man, is that state in which he enjoys as many of the good things, and suffers as few of the evils incident to human nature as possible; passing his days in a smooth course of permanent tranquility. A wise man, though deprived of sight or hearing, may experience happiness in the enjoyment of the good things which yet remain; and when suffering torture, or laboring under some painful disease, can mitigate the anguish by patience, and can enjoy, in his afflictions, the consciousness of his own constancy.

τὸ φρικωδέστατον οὖν τῶν κακῶν ὁ θάνατος οὐθὲν πρὸς ἡμᾶς͵ ἐπειδήπερ ὅταν μὲν ἡμεῖς ὦμεν͵ ὁ θάνατος οὐ πάρεστιν͵ ὅταν δὲ ὁ θάνατος παρῇ͵ τόθ΄ ἡμεῖς οὐκ ἐσμέν.

This happy state can only be obtained by a prudent care of the body, and a steady government of the mind. The diseases of the body are to be prevented by temperance, or cured by medicine, or rendered tolerable by patience.