And so we ought always to remain shut up in our cell. For whenever a man has strayed from it and returns fresh to it and begins again to live there he will be upset and disturbed. For if he has let it go he cannot without difficulty and pains recover that fixed purpose of mind, which he had gained when he remained in his cell; and as through this he has gone back, he will not think anything of the advance which he has missed, and which he would have secured if he had not allowed himself to leave his cell, but he will rather congratulate himself if he finds that he has regained that condition from which he fell away. For just as time once lost and gone cannot any more be recovered, so neither can those advantages which have been missed be restored: for whatever earnest purpose of the mind there may be afterwards, it will be the profit of the day then present, and the gain that belongs to the time that then is, and will not make up for the gain that has been once for all lost.