What do we learn from "Al Mah Yis'onen Adam Chai Gever Al Chata'av"?
Kidushin 80b #1: Even at a time of Aninus (mourning), one must be Misgaver on (overpower) his Yetzer Ra. If not, it will be Misgaver on him.
Kidushin 80b #2: This discusses one who complains about Hashem's ways. "Can a living man (justifiably) complain 1 ? Did he overcome his (temptations to) sin?!" It suffices that he is alive!
Rashi: One should bewail his sins - they bring the evil on him!
Ibn Ezra: This is from the root "Aven" (sin) - speaking sinful matters, like "k'Mis'onenim" (Bamidbar 11:1). A proof is "va'Yishma Hashem" (ibid.; this shows that it was spoken).
Orchos Tzadikim (Sha'ar ha'Da'agah DH v'Atah): This is a good kind of worry. A sinner must increase sadness and bitterness of heart that he rebelled against the One who formed everything.
Palgei Mayim #1: One who is at the level of Chai 2 , he should not complain about Hashem. Rather, he should overpower his sins. They do evil to him!
Palgei Mayim #2: He conquers his Yetzer and overpowers it. He should not complain about afflictions that come on him, since it was explained above that everything is a decree from Hashem. Hashem is not suspected to punish unjustly!
Lev Eliyahu (Shemos p.77): Even if one has only a Revi'is of blood, he is in a bed like a Golem and cannot move a limb, and can swallow only a little milk, he should not complain. He should rejoice that he is alive! He should be pained over his Chata'im, and all the more so over his Mezid sins!
Brachos 18a-b: Tzadikim are called alive even when they are dead. "Veha'Mesim Einam Yod'im Me'umah" - Resha'im are called dead even while alive.
Why is "Chata'av" written without a Yud?
R. Avigdor: The Kesiv is singular, to teach that one should worry even about one sin. In the Midbar, Bnei Yisrael tested Hashem 10 times (Bamidbar 14:22), therefore Hashem swore about the 10 [evil] Meraglim 1 , and corresponding to them enacted 10 days of Teshuvah to bewail one's sins 2 .
They died promptly in an evil plague (Bamidbar 14:37). We do not find that Hashem swore about them! Perhaps he means that Hashem swore about the people who accepted the words of the 10 evil Meraglim. (PF)
Since our verse discusses bewailing one's sins, R. Avigdor explains why Chazal enacted 10 days for this. Or, this shows how much one must worry about one sin - a sin of [Dasan and Aviram with] the manna is called testing Hashem (Erchin 15a)! Alternatively, he expounds why it is pronounced as if it has a Yud. (PF)