godan verb (-mu), transitive verb
assume; take for granted; jump to the conclusion
Used when someone firmly decides something is true without sufficient evidence, often with a negative connotation of being presumptuous or stubborn.
彼は私が賛成すると決め込んでいる。
He takes it for granted that I will agree.
まだ結果が出
It's too early to jump to the conclusion that it's a failure when the results aren't out yet.
godan verb (-mu), transitive verb
Often used with nouns or adjectives to indicate acting as if one were something or in a certain state, e.g., 知らん顔を決め込む (pretend not to know).
彼は知らん顔を決め込んで、質問に答えなかった。
He pretended not to know and didn't answer the question.
彼女は被害者を決め込んでいるが、実は加害者だ。
She poses as a victim, but in fact she is the perpetrator.
godan verb (-mu), transitive verb
persist in doing; go through with; make up one's mind to do
Emphasizes a strong determination to carry out a decision, often despite obstacles or criticism. Can imply stubbornness.
彼は反対されても自分の計画を決め込んだ。
He persisted in carrying out his plan despite opposition.
一度決め込んだら、彼は絶対に諦めない。
Once he makes up his mind, he never gives up.