と思い込んでしまう
to omoikonde shimau
JA
To mistakenly believe something, to become convinced of a wrong idea without realizing it
彼は自分が正しいと思い込んでしまう。
He mistakenly believes he is right.
Etymology
This phrase combines the quotative particle と, the verb 思い込む (omoikomu, 'to be convinced, to believe firmly') with the directional particle んで, and the auxiliary verb しまう (shimau), which conveys a sense of completion or an unintended, regretful outcome. It developed from Middle Japanese combinations of these grammatical components.
Memory Aid
Break it down: と marks what you're thinking, 思い込 means 'firm belief', and しまう adds the sense of it happening unintentionally. Together, it means you've ended up mistakenly believing something.
Collocations
誤ってと思い込んでしまう無意識にと思い込んでしまう自分でと思い込んでしまう
Synonyms
信じ込んでしまう決め込んでしまう
Antonyms
疑っているわからない迷っている
Related Words
思い込み思い込むしまう誤解確信