a big fish in a small pond
US /ə bɪɡ fɪʃ ɪn ə smɔl pɑnd/
UK /ə bɪɡ fɪʃ ɪn ə smɔl pɑnd/

1.
小さな池の大きな魚, 狭い世界での重要人物
a person who is important in a small group or organization but who would have much less importance in a larger, more competitive group or organization
:
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He was a big fish in a small pond at his old company, but now he's just one of many at the new multinational corporation.
彼は以前の会社では小さな池の大きな魚だったが、新しい多国籍企業では多くのうちの一人に過ぎない。
•
She prefers to be a big fish in a small pond, where her contributions are highly valued and recognized.
彼女は、自分の貢献が高く評価され認識される小さな池の大きな魚であることを好む。