9 Let us obey then, and let us think of this continually, that even as to the bird caught in the snare, wings are of no service, but he beats them about vainly, and to no purpose; so also to you there is no utility in your reasonings, when once you are powerfully captivated by wicked lust, but struggle as much as you may, you are captured! For this reason wings are given to birds; that they may avoid snares. For this reason men have the power of thinking; that they may avoid sin.
What pardon then, or what excuse will be ours, when we become more senseless than the brutes? For the bird which has once been captured by the snare, yet afterwards escaped, and the deer which has fallen into the net, but has broken through it, are hard to be captured again with the like; since experience becomes a teacher of caution to every one. But we, though often snared in the same nets, fall into the same again; and though honoured with reason, we do not imitate the forethought and care of the irrational animals!
Hence how often do we, from beholding a woman, suffer a thousand evils; returning home, and entertaining an inordinate desire, and experiencing anguish for many days; yet, nevertheless, we are not made discreet; but when we have scarcely cured one wound, we again fall into the same mischief, and are caught by the same means; and for the sake of the brief pleasure of a glance, we sustain a kind of lengthened and continual torment. But if we learn constantly to repeat to ourselves this saying, we shall be kept from all these grievous evils.
Source: Homilies on the Statues (New Advent)