As the title says, the main character has become so stupid and inept that the story was so painful to get through. There were many occasions, sometimes multiple times in a single chapter where information was given to the main character and then a literal minute later, probably on the same page if it was seen in the book itself, the character forgets that the was told or learned the information. Thus he makes illogical choices that by simply ignoring or forgetting the information he was told. He ended up in so many bad situations due to this; situations that could have easily been avoided.
I should say that despite this trainwreck of a story, the narrator did a good job.