You tell 'em Nao-chan. I don't know what it is, but you tell 'em.
Tbh, I think the whole "amnesia" thing with Sensei is actually just him blocking things out at will.
Virtually everything with Maya, Niki, and Sekai wouldn't work if his memories were actually erased.
It's even been implied that what he does learn about his past just goes in one ear and out the other:
Overall: I don't buy that Sensei's memories (of his past at least) were actually erased. He's probably just running from/ignoring them until he can't, or is forced to confront/need them. Things like Sekai haunting him, keeping Ami's picture in his pocket this whole time, and never even trying to remember his name, wouldn't make much sense if his memory was actually erased.
There's a reason Niki didn't really buy it:
Sensei forgetting past Resets wouldn't be farfetched, but just forgetting basically everything always seemed to be a little
convenient.
Also, on the topic of memories, I'd like to quote The Joker because I liked the comic for the most part (the movie can eat a nuke):
Nevertheless, I think Sensei just doesn't want to face his memories. Too much responsibility and pain, even now. He also seems to feel guilt over his past with Maya, in particular, but what brought this on after years of indulgence, is the real mystery. Possibly related to why the Resets even began.
Maya could definitely be the catalyst and we're still not sure why we see Maya hanging from a rope:
As for the mantra, yeah, I can see Maya grooming Sensei into thinking like that. She's not exactly above saying things like this:
Albeit, I wonder where she learned this from..