After the eigel hazahav (Golden Calf), everyone was downcast because they had lost favor in the eyes of Hashem. The general mood was repentance, remorse, and humility. Yet at that time Moshe Rabbeinu put in some of his greatest requests that he ever made of Hashem.
It's remarkable that these great entreaties of his were not made at a more auspicious time, when they were in favor with Hashem. He could have made them at the receiving of the Torah, when Hashem was so pleased with His people. At that time Moshe Rabbeinu should have put in a request.
But the Chovos Halevavos teaches us that sometimes a sin can help a man become better than a mitzvah. And he explains if somebody because of virtuous deeds,maasim tovim, begins to feel a certain pride, he becomes somewhat puffed up, then he loses status with Hashem because he is now being bereft of that grand quality of humility.
Humility is one of the most glorious attributes of mankind. But if, because of your righteous behavior, you are impelled to lose some of your humility, it doesn't pay. And therefore in some cases, he says, a good deed can do a man harm and a sin sometimes can do him great benefit.
If he feels so downcast because of his sin, he's so disheartened and he despises himself because of what he did, and he is contrite and he comes with humbleness before Hashem, that is an achievement that can outweigh by far any harm he did by his sin.
(Now don't go doing sins in the hope that you'll become humble. Try to become humble while you're becoming a big lamdan (scholar) or while you're making a lot of money. When you are riding on the wave of hatzlacha(success), that's the time you should be humble.) (Tape 579)