おばあさん：「私の財布の中に入れておいた1万円札がない。きっと誰かが盗んだんだよ」
娘：「おばあちゃん、きっと思い違いよ。誰も盗んだりしないから」
Omoichigai
Obaasan: Watashi no saifu no naka ni irete oita ichiman-en satsu ga nai. Kitto dare ka ga nusundan da yo.
Musume: Obaachan, kitto omoi chigai yo. Dare mo nusundari shinai kara.
Grandma: The 10,000 yen bill I putin mypurseis gone! Somebody must've stolen it.
Daughter: Grandma, I'm sure you've just got it wrong. No one's going to go and steal your money.
* * *
Omoichigai means to think something is true which isn't.
I've known the grandma in our neighborhood since childhood. She was the shamisen teacher, always smartly dressed in kimono, and very strict with her pupils-along with the sound of shamisens, we could always hear her as she scolded her students. A few years ago, though, she started to go senile. Her memory of recent events was the first thing to go, the conversation above being an example. She'd forgotten she'd already used tfie money. Her daughter at first thought, "Obaasan no omoichigai desho" ("It was just a little misunderstanding, I'm sure.") She'd thought this because, omoichigai wa dare ni demo aru (everyone gets things confused sometimes.) Un fortunately, however, when the old woman's son visited
her after a long absence, she didn't know who he was.
"Excuse me, young man, what was your name again?" she'd asked. You can imagine how surprised he was. It was time to take her to the doctor. The diagnosis was Alzheimer's disease for which there are no specific treatments; the disease just slowly runs its course, the patient progressively getting worse. What a shock for the family. The grandma, however, was like a child again. She would get up in the middle of the night and take a walk, thinking it was the afternoon. In the end, the family couldn't take care of her and so had her hospitalized. A nurse at the hospital, "Watashi no koto wo musume san to omoichigai shiteru'n desu yo" ("She's a bitconfused, sometimes thinking I'm her daughter." )
Though I haven't met her for some time now, I think I'd prefer to remember her as the lovely woman dressed in kimono who teaches the shamisen. How hard to see her now, unable to go to the bathroom herself, always wearing diapers. It's truly pathetic what the disease can do. It takes away the honor and achievements of a lifetime, the dignity of being a human.
Some other examples where, "Sore wa anata no omoichigai desu yo" is appropriate:
・the shopping bag doesn't contain the thing you thought you'd bought-"You must have misunderstood. "
・you find out the person you thought liked you, doesn't-"It was all in your head."
・you misinterpret what someone says - "You've got it all wrong." Watashi wa omoichigai wo yoku shimasu (I often get things mixed up.) How about you?