Excessive joy and very keen suffering always occur in the same person, for they condition each other reciprocally, and are also in common conditioned by great activity of the mind. Both are produced, as we have just seen, not by what is really present, but by the anticipation of the future. But since pain is essential to life, and its degree is also determined by the nature of the subject, sudden changes, because they are always external, cannot really alter its degree. Thus an error and delusion always lies at the foundation of immoderate joy or grief, and consequently both these excessive strainings of the mind can be avoided by knowledge. Every immoderate joy (_exultatio, insolens lætitia_) always rests on the delusion that one has found in life what can never be found there—lasting satisfaction of the harassing desires and cares, which are constantly breeding new ones. From every particular delusion of this kind one must inevitably be brought back later, and then when it vanishes must pay for it with pain as bitter as the joy its entrance caused was keen. So far, then, it is precisely like a height from which one can come down only by a fall. Therefore one ought to avoid them; and every sudden excessive grief is just a fall from some such height, the vanishing of such a delusion, and so conditioned by it. Consequently we might avoid them both if we had sufficient control over ourselves to survey things always with perfect clearness as a whole and in their connection, and steadfastly to guard against really lending them the colours which we wish they had. The principal effort of the Stoical ethics was to free the mind from all such delusion and its consequences, and to give it instead an equanimity that could not be disturbed. It is this insight that inspires Horace in the well-known ode— “_Æquam memento rebus in arduiis_ Servare mentem, non secus in bonis _Ab insolenti temperatam_ _Lætitia._” For the most part, however, we close our minds against the knowledge, which may be compared to a bitter medicine, that suffering is essential to life, and therefore does not flow in upon us from without, but that every one carries about with him its perennial source in his own heart. We rather seek constantly for an external particular cause, as it were, a pretext for the pain which never leaves us, just as the free man makes himself an idol, in order to have a master. For we unweariedly strive from wish to wish; and although every satisfaction, however much it promised, when attained fails to satisfy us, but for the most part comes presently to be an error of which we are ashamed, yet we do not see that we draw water with the sieve of the Danaides, but ever hasten to new desires. “_Sed, dum abest quod avemus, id exsuperare videtur_ _Cætera; post aliud, quum contigit illud, avemus;_ _Et sitis æqua tenet vitai semper hiantes._”—LUCR. iii. 1095.