One should not grow frustrated if, after he resolved to avoid forbidden speech, his evil inclination got the better of him and he spoke loshon hora. Even if this happens time and again, nevertheless, he should not despair. Rather, he should forever strengthen himself to avoid improper speech, and persevere. This is how one should conduct himself his entire life.
This is the intent of the Talmud’s statement, “One should forever arouse his good inclination to subdue his evil inclination” (Berachos 5a). Life is an ongoing struggle with one’s evil inclination. One must forever be poised for battle and never be discouraged by failure. With knowledge of what the Torah requires of us and proper resolve, our efforts will ultimately succeed. ~ Chofetz Chaim