Satan is the enemy of mankind. He tries to make humans to go astray from the right path. Of course there are big disappointments for those  who fell in to its traps. These disappointments come in different degrees and levels. Small mistakes result in small

disappointments, and big mistakes result in big sufferings. Whether it's a mistake or conscious diversion, if the person repents for his bad deed and comes to the right path, Allah will accept his repentance and will forgive him.  He is most forgiving and most merciful. The most important thing is; man has to acknowledge his mistakes, show regret and keep himself on the straight path in the future.
Therefore, the man's duty is; by following the light and the guidance of Allah, always aim goodness and spiritual heights. He may stumble on the way and fell into pit holes from time to time.
Although the descent of Adam from the heaven is the consequence of his mistake of obeying Satan,  he was given a second chance on the earth to repent for what he has done. This world is a temporary place for trial, its up to the humans to use his God given abilities to follow the right path.
Allah says: "We "said "Down with you all from this state" as He reminds us His authority and punishes everyone who disobeys His order as in the case of Adam, Eve and Satan. But as Adam and Eve repented from what they did, Allah embraced them with clemency and thus uses "Me" giving humanity mercy and assurance and reminds them: "there shall none the less, most certainly come unto you Guidance from Me: and those who follow my Guidance need have no fear, and neither shall they grieve". Of course this is pointing at the end and the result of the trial which requires patience and strength on doing good deeds. It also inspires us not to give in, if there are solvable obstacles on the way.
In spite of the past experiences and innate abilities, if the opportunities of this trial are missed by ignoring God's signs and His light and insists on his wrongdoing, then Man’s  inescapable end will be the hellfire. His deliberate and insistent choice of wrongdoing will be the cause of his eternal fall.
With a layman's logic, this is what I understood from the above verses. Allah knows best.
Selaam to you all.
M. Selami Çekmegil, Translation: Vakkas TEKÄ°N