St. John of the Cross in the Ascent of Mount Carmel,

"You should take care always to be inclined

not to the easiest thing, but to the hardest;

not to the tastiest, but to the most insipid;

not to the things that give the greatest pleasure, but to those that give the least;

not to the restful things, but to the painful ones;

not to consolation, but to desolation;

not to more, but to less;

not to the highest and dearest, but to the lowest and most despised;

not to the desire for something, but to having no desires.”