ものと思っていた

ものとおもっていた

Was under the impression that, Had (always) assumed that

犬いぬは怖こわいものと思おもっていたけど、飼かってみたら思おもったより優やさしかった。

I was under the impression that dogs were scary, but after I tried taking care of one, they turned out to be more gentle than I had thought.

Explanation

「ものと思っていた」 means 'I had taken it for granted that ..., but reality turned out otherwise'.

It often goes with 「てっきり」 or 「すっかり」, and carries surprise, embarrassment or sudden realization on finding the truth.

「てっきり今日休みのものと思っていました」 (I was sure today was a day off).

It is used to explain a misunderstanding or mistake, or in a character's inner thoughts. A more polite form is 「ものと思っておりました」.

Mixed up with

「と思っていた」: only says what you thought in the past; it need not clash with reality.

「ものと思っていた」: you took it as obvious, and what follows shows the opposite. It often pairs with 「てっきり」, a clue in exams.

「つもりだった」: about your own intention or impression, often used to excuse an oversight, as in 「メールを送ったつもりだった」 (I thought I had sent the email).

Examples

お母かあさんに怒おこられるものと思おもっていたが怒おこられず、拍子抜ひょうしぬけした。
I was under the impression that my mom would scold me, but she didn't, which was anticlimactic.
子供こどもの頃ころ、森もりで迷まよって、てっきりこのまま死しぬものと思おもっていたが、無事ぶじに助たすけられた。
As a child I got lost in a forest. I was sure I would die there, but I was rescued.
てっきり漢字かんじを学まなぶのは退屈たいくつなものと思おもっていた。
I had assumed that learning kanji would be boring.
え...まだ晩御飯ばんごはん食たべてないの？てっきり帰かえりに食たべてくるものと思おもっていたから、あなたの分ぶんは作つくってないですよ。
What… You haven't eaten dinner yet? I was totally under the impression that you were going to grab something on the way back home, so I did not make anything for you.
私わたしの母ははは猫ねこが好すきではないものと思おもっていたが、聞きいてみたらただ猫ねこアレルギーがあるそうだ。
I was under the impression that my mother did not like cats, but after asking her, I found out that it's just that she is allergic to them.
ゲートボールは老人ろうじんしかやらないものと思おもっていたが、最近さいきんは若者わかものの間あいだで流行はやっているらしい。
I was under the impression that gateball was something only old people played, but it seems to be popular among young people these days.
面接めんせつに合格ごうかくするものと思おもっていたが不合格ふごうかくとなり、愕然がくぜんとしている。
I was sure I would pass the interview, but I failed, and I'm stunned.
雷かみなりに打うたれて死しぬものと思おもっていたが、どうやら生いき残のこったようだ…。
I thought I'd be killed by the lightning, but it seems I survived...
ワンピースは若わかい子こしか着きられないものと思おもっていたが、意外いがいと私わたしでも着きられる。
I always used to think that only young girls could wear dresses, but unexpectedly, even I can wear them.
強盗ごうとうに殺ころされるものと思おもっていたが、意外いがいにも強盗犯ごうとうはんは傷きず一ひとつつけてこなかった。
I was sure the robber would kill me, but surprisingly he didn't leave a single scratch on me.
雨あめの日ひはついていないものと思おもっていましたが、雨あめの日ひは雨あめの日ひなりに楽たのしいことがあります。
I always used to think that rainy days were unlucky, but rainy days are fun in their own way.
私わたしは彼かれが拒否きょひするものと思おもっていたが、予想よそうとは逆ぎゃくに彼かれは賛成さんせいした。
I was sure he would refuse, but contrary to my expectations he agreed.
Ａ：「彼女かのじょが負まけたなんて驚おどろいたな。きっと勝かつものと思おもっていたけど。」Ｂ：「わたしもそう思おもってた。」
A: 'Surprisingly, she lost. I was under the impression that she would win.' B: 'I thought so too.'