stew in one's own juice

Momoは大人が "men in grey" に時間を奪われていると気づき、子供達を中心に時間を取り戻すためのデモを行い、皆にamphitheaterに集まることを呼びかけましたが、誰も現れません。
Franco was next to leave. 'It's hopeless,' he said. 'We can't count on the grown-ups, we know that now. I never did trust them anyway. As far as I'm concerned, they can stew in their own juice from now on.'
"stew in their own juice" は慣用句に違いありません。意味を調べます。
・McGraw-Hill Dictionary of American Idioms and Phrasal Verbs: to be left alone to suffer one's anger or disappointment. John has such a terrible temper. When he got mad at us, we just let him go away and stew in his own juice. After John stewed in his own juice for a while, he decided to come back and apologize to us.
・Cambridge Idioms Dictionary: if you leave someone to stew in their own juice, you leave them to worry about something bad that has happened or something stupid they have done She'll calm down - just leave her to stew in her own juices for a bit.
なるほど、"stew in their own juice" ですね。この手は自分で反省できる人間には有効ですが、反省できない人もいるので困ることがあります。