From Jewish with Feeling: Meaningful Jewish Practice, by Rabbi Zalman Schachter-Shalomi:
The Hasidim tell of Reb Levi Yitzchak of Berditchev, who used to say, before he went to sleep at night, "Master of the Universe, today I didn't do so well. I promise that tomorrow I'm going to do better."
Immediately he would chide himself. "But Levi Yitzchak, that's what you said last night!"
"Ah, but tonight," he'd reply to himself, "tonight I really mean it."