However, even after years of striving for inner change, at times the person may be unpleasantly confronted with the realization that his inner self is far, very far, from having been transformed. In a moment of temptation or provocation he loses control, and at that moment all his refined and holy thoughts vanish without a trace. He feels the same raw and wild character traits coursing through him that were there “from his youth” and even “from the moment he stirred to leave the womb” (as referred to in the post linked to above).
This discourages him from striving to change himself. He wonders despairingly, “Of what value were all these years of effort?” He feels like a miserable failure, and wishes to “surrender” in the fight against the evil inclination.
Yet these very doubts are in fact a devious ploy of the evil inclination, and for several reasons:
1) Striving to improve one’s character traits is part of serving Hashem. One should not serve Hashem “for the sake of receiving a reward” (Avos 1:3)—not even for the reward of feeling fulfilled at succeeding in refining oneself. One should strive to improve oneself simply because this is the will of Hashem. Of course, if one reaches the point at which he feels confident that his efforts have borne fruit, so much the better. However, this is only a bonus, and not the reason that one should strive for self-refinement.
2) In reality, over time the person has changed. If he examines himself honestly and compares himself as he is now to the way he was before he decided to devote himself earnestly to serving Hashem and improving himself, he will surely notice a significant change. Beforehand, his ugly character traits were far more severe, and over time, the frequency of occasions in which he lost control diminished, as did the intensity of these desires. He has also significantly developed positive, noble character traits that hardly existed before.
Although the person’s old bad traits still emerge from time to time, and this is a cause for concern, this is not a cause for despair. It is simply an indication that more work remains for him to do—and this is why his soul is still in his body.
3) Hashem created the person’s evil inclination for a reason—in order for the person to be tested by struggling against it. This struggle is most likely meant to continue for the person’s entire life, until his last breath, for only very few reach the level of the Tzaddik, who has vanquished his evil inclination altogether. Moreover, the very fact that the person can even entertain the thought that such base desires do not befit him indicates that he doesn't know his place, for it is simply not his mission in life to reach the level of Tzaddik, and he is destined to struggle with his evil inclination in one form or another.
Rather, his mission is to perform Iskafya. Every act of Iskafya brings Hashem tremendous pleasure, and draws a powerful divine light upon the person. And the main thing is that he fulfills the purpose for which he was created.
With Hashem’s help, the person’s efforts will also bear fruit, and he will transform his inner self to a certain degree, to the point that he will struggle in more subtle areas than he did before. Yet even if one never reaches this point, or does not succeed to the degree he had hoped and aimed for, it doesn’t matter. The main thing is not the nature of the person’s struggle, but his effort. Thus, the one who exerts great effort to overcome a base desire is in a sense superior to the one who performs exceptionally good deeds without effort. As long as the person is struggling, he is fulfilling his purpose in the world.
Based on Tanya chs. 15, 27, 29, 35, classes from my Mashpi’im, and other sources.