A life of avodas Hashem abounds with challenges. One especially important and trying challenge is to avoid despair. Virtually everyone, at some point in his life, stumbles and suffers spiritual setbacks. It is not uncommon for a person to experience a period of yeridah (decline) in his life. At such times, negativity develops momentum and a person can encounter the challenge of not despairing. What perspectives / kochos hanefesh help us to successfully navigate this crucial challenge?
Ramban (in his introduction to sefer Devarim) directly addresses our question. In the opening segment of his speech Moshe Rabbeinu, explains the Ramban, set out "to strengthen their (i.e. Bnei Yisroel's) heart, by informing them that Hashem will always relate to them with the attribute of mercy - so that a person should not say that we will be unable to take possession of Eretz Yisroel because there is no one who does not sin and immediately the attribute of justice will be applied to us and we shall perish. Therefore, Moshe Rabbeinu informed them that Hakadosh Baruch Hu is merciful, abounding with mercy, because [the prospect of] forgiveness and pardon from Him aides and assists people in His service, as Scripture states 'forgiveness is with you in order that you be feared'". In a word, the omnipresent possibility of teshuva[1] and the concomitant prospect of forgiveness dispel despair. Forgiveness and the promise of a new beginning allow hope to dispel despair.
A second vital perspective emerges from various pesukim in sefer Devarim. Amongst them is the passuk, "ubacharta bachaim lemaan tichye atta vzarecha - you shall choose [the path of] life, so that you and your descendants may live". In other words, Hakadosh Baruch Hu wants us to succeed. Accordingly, Hakadosh Baruch Hu gives us the resources and resourcefulness to succeed.
Thus, belief in Hakadosh Baruch Hu breeds self-confidence. If one reflects upon his belief in Hashem he will be buoyed by self-confidence, and the prospect of despair will fade.
A final perspective may be gleaned from a comment of Rashi in this week's parsha. Rashi comments that the Torah charges us to love Hashem (and not merely fear Him) because "One who serves at his master's side out of love can not be compared to one who serves out of fear. One who serves at his master's side out of fear once the master overburdens him he leaves [the master] and goes off" (Artscroll, Saperstein edition translation). One who is motivated by love is also energized by love and never relents, regardless of how daunting the challenge may be. We have opportunity to see the truth and astuteness of Rashi's comment (from the Sifrei) by observing the heroic, steadfast devotion of parents for a sick, troubled, or handicapped child. The challenge of coping with such a child can be very formidable, and yet parents preserve. The reason is simple: in the presence of love despair is unimaginable. If one is able to cultivate a feeling of love for Hakadosh Baruch Hu - because of who He is, what He does for us at all times, etc. - we will always persevere in His service. Despair / yei'ush, as the Rebbe of Kotzk taught, is shelo midaas - an uninformed reaction due to lack of reflection.
[1]The Yerushalmi in Maseches Peah teaches that one can always do teshuva. Rambam's comments in Hilchos Teshuva regarding Sichon, Pharoh, et. al. lie beyond the purview of the present dvar Torah.