6. As for the first, it is plain that the appetites are wearisome and tiring. They resemble little children, restless and hard to please, always whining to their mother for this thing or that, and never satisfied. Just as anyone who digs covetously for a treasure grows tired and exhausted, so does anyone who strives to satisfy the appetites' demands become wearied and fatigued. And even if a soul does finally fill them, it is still always weary because it is never satisfied. For, after all, one digs leaking cisterns that cannot contain the water that slakes thirst. As Isaiah says: Lassus adhuc sitit, et anima ejus vacua est, which means: He is yet faint with thirst and his soul is empty [Is. 29:8].
A soul with desires wearies itself, because it is like someone with a fever whose thirst increases by the minute, and who feels ill until the fever leaves. It is said in the Book of Job: Cum satiatus fuerit, arctabitur, aestuabit, et omnis dolor irruet super eum (When he has satisfied his appetite, he will be more burdened and oppressed; the heat of appetite will have increased and every sorrow will fall upon him) [Jb. 20:22].
The appetites are wearisome and tiring because they agitate and disturb one just as wind disturbs water. And they so upset the soul that they do not let it rest in any place or thing. Isaiah declares of such a soul: Cor impii quasi mare fervens (The heart of the wicked is like a stormy sea) [Is. 57:20]. And anyone who does not conquer the appetites is wicked.
People seeking the satisfaction of their desires grow tired, because they are like the famished who open their mouths to satisfy themselves with air. But they find that instead of being filled the mouth dries up more since air is not one's proper food. With this in mind Jeremiah says: In desiderio animae suae attraxit ventum amoris sui (In the appetite of his will he drew in the air of his attachment) [Jer. 2:24]. To comment on the dryness in which the soul is left, he immediately adds the advice: Prohibe pedem tuum a nuditate, et guttur tuum a siti. This means: Hold back your foot (that is, your mind) from nakedness, and your throat from thirst (that is, your will from satisfying its desire, which only causes greater thirst) [Jer. 2:25].
Just as a lover is wearied and depressed when on a longed-for day his opportunity is frustrated, so is the soul wearied and tired by all its appetites and their fulfillment, because the fulfillment only causes more hunger and emptiness. An appetite, as they say, is like a fire that blazes up when wood is thrown on it, but necessarily dies out when the wood is consumed.
7. In regard to the appetites, things are even worse. The fire dwindles as the wood is consumed, but the intensity of the appetite does not diminish when the appetite is satisfied, even though the object is gone. Instead of waning like the fire after the wood is burned, the appetite faints with fatigue because its hunger has increased and its food diminished. Isaiah refers to this: Declinabit ad dexteram, et esuriet; et comedet ad sinistram, et non saturabitur (He will turn to the right and be hungry, and eat toward the left and not be filled) [Is. 9:20]. When those who do not mortify their appetites turn to the right, they of course see the abundance of the sweet spirit that is the lot of those who are at the right hand of God but is not granted to them. When they eat at the left (satisfy their appetite with some creature), they of course grow discontented because, in turning from what alone satisfies, they feed on what augments their hunger. It is clear, then, that the appetites weary and fatigue a person." THE ASCENT OF MOUNT CARMEL Chapter 6 by St. John of the Cross