When we draw water from a well, it can happen that we inadvertently also bring up a frog. When we acquire virtues we can sometimes find ourselves involved with the vices which are imperceptibly interwoven with them. What I mean is this. Gluttony can be caught up with hospitality; lust with love; cunning with discernment; malice with prudence; duplicity, procrastination, slovenliness, stubbornness, wilfulness, and disobedience with meekness; refusal to learn with silence; conceit with joy; laziness with hope; nasty condemnation with love again; despondency and indolence with tranquillity; sarcasm with chastity; familiarity with lowliness. And behind all the virtues follows vainglory as a salve, or rather a poison, for everything.

Saint John of the Ladder, The Ladder of Divine Ascent, Step 26, “On Discernment”