"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." (the Ascent of Mount Carmel, pg 132)
As a mother, I totally understand what St. John is talking about! For example, I go into Target firmly resolved to keep to my list. "This is a quick shopping trip for Baby Tess," I announce loudly. "We are not here to get things for ourselves."
My three year old immediately grabs a small overpriced packet of gold fish crackers. "She's a good girl," I rationalize. "She deserves a gift." I cheerfully give her permission to buy it. But now I've fed her roaring appetite. She's no longer satisfied with goldfish crackers. She wants marshmallows, and cookies, and chocolate popsicles. She wants them ALL, she's not content to trade up or down. Before I know what hits me, she's having a melt down over my denial of a $45 Barbie computer. All this drama which began over a $1 goldfish snack attack.
I think St. John is telling us that if we start indulging in our appetites we will never be satisfied, just like my three year old in Target.