The Sefer V'Ha'er Eineinu quotes Rav Shlomo Zalman Auerbach, ZTs"l thus:
"Even if one only has instances of stumbling, without any successes whatsoever [in his struggle to break from of his lusts]; but he at least has the will and desire to become metukan in his shmiras einayim (i.e. to correct his erstwhile heinous passion for immodest gazing)," says Rav Shlomo Zalman: "he should rejoice with tremendous happiness that he is infused with this holy, pure desire, and he should remember that every time that his soul awakens with this ambition, the creates a profound nachas ruach for the Kadosh Baruch Hu."
I've found that it's that one victory that can lead to the next. Mitzvah goreres mitzvah. For me, when I am matzliach in shmiras einayim, and resist the temptation to indulge in my passions and taavos, that is a perfect time to ask for an extra jolt of siyatta d'shmaya to continue to succeed. [Like mamisch right now, as we are reading and thinking about this, and not indulging in our taavos].
So even if I fail once in a while, and lose the impetus to resist, and stam give in to my taavos, I know that I at least have this once success from before, plus this bakasha, plus the charata of a failure -- three separate categories of mitzvah in overcoming and defeating taavah.
(see further, V'Ha'er Eineinu, p. 75-76)