Why is despair not an approved state?

Despair is unthinkable for a person who is aware of the fact that Allah is the creator of every being and every event, and who measures the power of Allah by its true measure. Because Allah is the One Who removes difficulties for His servants, is most forgiving, is full of mercy and has complete power and knowledge. Every incident that people may regard as a reason for despair, including all impediments, unexpected obstacles, diseases, accidents or mistakes, in fact occurs under the complete control of Allah. Allah is All-Knowing and nothing is absent from His knowledge. Being aware that one’s destiny is designated by His endless knowledge is the greatest comfort one can ever have. Knowing this fact, one can never give way to despair.

Besides this, believers, knowing that it is possible that their mistakes may be remitted in this world, do not lose hope. Indeed, people are commanded in the Qur’an not to despair of the mercy of Allah:

“… Do not despair of solace from Allah. No one despairs of solace from Allah except for those who disbelieve. “ (Surah Yusuf, 87)

Say: “My servants, you who have transgressed against yourselves, do not despair of the mercy of Allah. Truly Allah forgives all wrong actions. He is the Ever-Forgiving, the Most Merciful.”   (Surat az-Zumar, 53)

Why is despair not an approved state?