elephant in the room

an obvious issue, problem, or matter that people purposely ignore

The idiom "elephant in the room" is believed to have originated in the 19th century. It is thought to have been inspired by a fable by Ivan Krylov, in which a man is so focused on examining small details that he fails to notice an elephant standing in the room. The phrase is used to describe an obvious problem or issue that everyone is aware of but no one wants to talk about.

The student's plagiarism was the elephant in the room in the classroom, but the teacher didn't want to embarrass the student in front of the class.
The family's unspoken tension was the elephant in the room during the holidays, but no one wanted to ruin the festive mood by bringing it up.
The company's financial problems were the elephant in the room at the meeting, but no one wanted to talk about it.
The country's political instability was the white elephant in the room at the international summit, but no one wanted to risk diplomatic relations by discussing it openly.
The elephant in the room in the relationship was the issue of trust, but neither partner wanted to have an honest conversation about it.