The practice of Humility - 34

If you do some extraordinary mortification, try to remain immune from the poison of vainglory, which often destroys all the merits; do that mortification for the right motive: because it is unbecoming for a poor sinner like yourself to live at your convenience and pleasure and because you have so many debts to pay before the divine justice.  Reflect that you need penitential works to check the violence of the passions, keeping you within the limits of duty, as bridle and bit are necessary to tame an impetuous horse.

J. Pecci (later Pope Leo XIII)