But he paused first, and he wouldn't look at me, so I thought he was messing with me. (1.155-157)
Grover has a hard time lying; it doesn't come easily to him. But he knows the importance of erasing Percy's memory of Mrs. Dodds.
"There was no way I was going to remember the difference between Chiron and Charon, or Polydictes and Polydeuces." (2.18)
Percy has a difficult time memorizing names and studying names and facts. Maybe that's his dyslexia and his attention deficit disorder kicking in.
I tried to square that with the fact that I seemed to remember…something about my father. A warm glow. A smile. (3.99)
Percy's memory is more powerful than the lies his mom would have him believe. There are some memories that you can't erase. Percy constantly must choose between thinking of his father as this warm glow or as a cold, indifferent god.
"Thank you, Percy," my mom said. "Once we get to Montauk, we'll talk more about …whatever you've forgotten to tell me, okay?" (3.74)
Percy's memory is being manipulated by Chiron, Grover, and Sally Jackson, who are all trying to protect him from knowing that he's a demi-god.
Mr. D (Dionysus)
"What will people think of your 'science' two thousand years from now?" Mr. D continued. "Hmm? They will call it primitive mumbo jumbo. That's what. Oh, I love mortals—they have absolutely no sense of perspective. They think they've come so-o-o far." (5.121)
The gods have a totally different understanding of memory by virtue of the fact that they have lived for so long and will live for so long. Their perspective on life is vastly different from a human's perspective. A human only really knows what has happened in his or her own lifetime. Is memory important to the gods? Do they care much about it?
I tried to remember the beginning of the school year. It seemed like so long ago, but I did have a fuzzy memory of there being another Latin teacher my first week at Yancy. Then, without explanation, he had disappeared and Mr. Brunner had taken the class. (5.83)
The gods and immortals are able to manipulate the human world in big ways. Chiron alters the course of Percy's life by becoming Mr. Brunner and by magically becoming a member of the Yancy academy. He manipulates Percy's memory of how things actually happen. Percy is immune to the Mist that generates when gods and monsters interact with the human world.
"Even I am not old enough to remember that, child, but I know it was a time of darkness and savagery for mortals. Kronos, the lord of the Titans, called his reign the Golden Age because men lived innocent and free of all knowledge. But that was mere propaganda. The Titan king cared nothing for your kind except as appetizers or a source of cheap entertainment. It was only in the early reign of Lord Zeus, when Prometheus, the good Titan brought fire to mankind, that your species began to progress, and even then Prometheus was branded a radical thinker." (10.68)
There are certain things that the gods can't remember very well – they haven't been around forever. Before them was the Golden Age of the Titans, which was definitely a brutal, horrible time. The gods do have a painful memory in their past of Kronos's reign. Perhaps this memory helps them rule better than he did.
"May the Fates forbid that the gods should ever suffer such a doom, or that we should ever return to the darkness and the chaos of the past. All we can do, child, is follow our destiny." (10.70)
Chiron understands that the only way to overcome fear is to move forward and go with the flow of life. Following one's destiny seems like it might involve letting go of the past. The gods' immortality make them very forward-thinking.
"She sacrificed herself to save us," he said miserably. "Her death was my fault. The Council of Cloven Elders said so." (16.69)
Grover carries his memory of Thalia and Thalia's death with him all the time. He feels such guilt for not being able to keep her alive. Even though his memory of Thalia is a painful one, remembering her seems to be a way of honoring her.
In the back of my mind, some small problem kept nagging at me. I'd had a dream or something…I needed to talk to my friends. But I was sure it could wait. (16.191)
The Lotus Casino does wonders to the memory – it completely sucks it out of guests who stay there, causing them to forget where they came from, where they were headed, or that time is even passing. It's an eerie trap that Percy and his friends fall into. Here, Percy describes what it feels like to have your memories sucked out you; it's almost as if memories are like prisoners locked far away and calling out to their owners. The Lotus Casino experience proves that memory is really important in helping demi-gods stay on task and finish their quests.