Letters from a Stoic 16 : 9

Natural desires are limited; but those which spring from false opinion can have no stopping-point. The false has no limits. When you are travelling on a road, there must be an end; but when astray, your wanderings are limitless. Recall your steps, therefore, from idle things, and when you would know whether that which you seek is based upon a natural or upon a misleading desire, consider whether it can stop at any definite point. If you find, after having travelled far, that there is a more distant goal always in view, you may be sure that this condition is contrary to nature. Farewell.